Document:

<PAGE>

                                                                     EXHIBIT 4.2

                               BOCA RESEARCH, INC.

         FIRST AMENDMENT OF 1996 NON-EMPLOYEE DIRECTOR STOCK OPTION PLAN

         In accordance with the provisions of Section 14 of the Boca Research,
Inc. 1996 Non-Employee Director Stock Option Plan (the "Plan"), the Plan is
hereby amended effective as of the date of stockholder approval hereof, as
follows:

         1. Section 4 of the Plan is hereby amended by deleting the Section 4 in
its entirety and replacing it in its entirety with the following:

         "Subject to the availability of shares of Common Stock under the Plan,
(i) an option to purchase 10,000 shares of Common Stock will automatically be
granted to each non-employee director on the date the amendment to the Plan is
approved by the shareholders of the Company; (ii) an option to purchase 10,000
shares of Common Stock will automatically be granted to each non-employee
director who is initially elected to the Board after the approval of the
amendment to the Plan by the shareholders, upon his or her election to the
Board; and (iii) an option to purchase 10,000 shares of Common Stock will be
granted to each non-employee director on the date of each meeting of the
shareholders of the Company at which such director is reelected to the Board. In
addition, the Chairman of the Board will receive an automatic grant of an option
to purchase an additional 5,000 shares of Common Stock under the following
circumstances: (i) an option will automatically be granted to the Chairman on
the date the amendment to the Plan is approved by the shareholders of the
Company; and (ii) an option will automatically be granted to the Chairman upon
his or her initial election to the Board or reelection as Chairman."

         2. The following new Section 7(b) of the Plan is hereby inserted and
the other sections are renumbered accordingly:

         "7(b) Options granted on and after the date of amendment of the Plan
shall vest in full on the date of grant and shall be fully exercisable."

         3. This Amendment shall take effect as of the date of its adoption by
the Board of Directors of Boca Research, Inc. and upon its approval by the
Stockholders of Boca Research, Inc. in accordance with the provisions of Section
14 of the Plan.

         4. Except as hereinabove provided, the Plan is hereby ratified and
confirmed in all respects.

                               Boca Research, Inc.
                               By: /s/ Robert W. Federspiel
                                   ------------------------
                                   Robert W. Federspiel
                                   Secretary

Adopted by the Board of Directors: January 5, 1998

Adopted by the Stockholders: May 18, 1998<PAGE>

                                                                     EXHIBIT 4.3

                               BOCA RESEARCH, INC.

        SECOND AMENDMENT OF 1996 NON-EMPLOYEE DIRECTOR STOCK OPTION PLAN

         In accordance with the provisions of Section 14 of the Boca Research,
Inc. 1996 Non-Employee Director Stock Option Plan (the "Plan"), the Plan is
hereby amended effective as of the date of stockholder approval hereof, as
follows:
         1. Section 2 of the Plan is hereby amended by increasing the number of
shares subject to the Plan from Two Hundred Thousand Shares (200,000) to Five
Hundred Thousand Shares (500,000) of the common stock, par value $.01 per share,
of the Corporation.
         2. Section 4 of the Plan is hereby amended by deleting each reference
to "10,000" therein and replacing the same with "12,000".
         3. This Amendment shall take effect as of the date of its adoption by
the Board of Directors of Boca Research, Inc. and upon its approval by the
Stockholders of Boca Research, Inc. in accordance with the provisions of Section
14 of the Plan.
         3. Except as hereinabove provided, the Plan is hereby ratified and
confirmed in all respects.

                                             Boca Research, Inc.

                                             By: /S/ ROBERT W. FEDERSPIEL
                                                 ------------------------
                                                 Robert W. Federspiel
                                                 Secretary

Adopted by the Board of Directors: February 21, 2000

Adopted by the Stockholders: May 22, 2000<PAGE>

                                                                    EXHIBIT 4.2

                               BOCA RESEARCH, INC.

                   SECOND AMENDMENT OF 1992 STOCK OPTION PLAN

         In accordance with the provisions of Section 19 of the Boca Research,
Inc. 1992 Stock Option Plan (the "Plan"), the Plan is hereby amended effective
as of the date of stockholder approval hereof, as follows:

         1. Section 2 of the Plan is hereby amended by increasing the number of
shares subject to the Plan from One Million Three Hundred Thousand Shares
(1,300,000) to One Million Seven Hundred Thousand Shares (1,700,000) of the
common stock, par value $.01 per share, of the Corporation.

         2. This Amendment shall take effect as of the date of its adoption by
the Board of Directors of Boca Research, Inc. and upon its approval by the
Stockholders of Boca Research, Inc. in accordance with the provisions of Section
19 of the Plan.

         3. Except as hereinabove provided, the Plan is hereby ratified and
confirmed in all respects.

                                      Boca Research, Inc.

                                      By: /s/ Robert W. Federspiel
                                          -------------------------------------
                                          Robert W. Federspiel
                                          Secretary

Adopted by the Board of Directors: February 6, 1996

Adopted by the Stockholders:       May 20, 1996<PAGE>

                                                                    EXHIBIT 4.3

                               BOCA RESEARCH, INC.

                    THIRD AMENDMENT OF 1992 STOCK OPTION PLAN

         In accordance with the provisions of Section 19 of the Boca Research,
Inc. 1992 Stock Option Plan (the "Plan"), the Plan is hereby amended effective
as of the date of stockholder approval hereof, as follows:

         1. Section 2 of the Plan is hereby amended by increasing the number of
shares subject to the Plan from One Million Seven Hundred Thousand Shares
(1,700,000) to such number of shares as shall always be equal to twenty-six
(26%) of the then issued and outstanding shares of the common stock, par value
$.01 per share, of the Corporation.

         2. This Amendment shall take effect as of the date of its adoption by
the Board of Directors of Boca Research, Inc. and upon its approval by the
Stockholders of Boca Research, Inc. in accordance with the provisions of Section
19 of the Plan.

         3. Except as hereinabove provided, the Plan is hereby ratified and
confirmed in all respects.

                                     Boca Research, Inc.

                                     By: /s/ Robert W. Federspiel
                                         --------------------------------------
                                         Robert W. Federspiel
                                         Secretary

Adopted by the Board of Directors: June 14, 1999

Adopted by the Stockholders:       August 16, 1999<PAGE>

                              AMENDMENT NUMBER ONE
                                       TO
                           LEASE SCHEDULE NO. 4125.03A
                                     BETWEEN
                      FINOVA CAPITAL CORPORATION ("LESSOR")
                                       AND
                       MOBILE PET SYSTEMS, INC. ("LESSEE")

I.       EQUIPMENT: Lessee and Lessor agree to cause the equipment leased and
         described as:

         One (1) Calumet Coach Company Model MMT-481P Siemens ECAT Mobile Pet
         Unit, VIN #1TKH04222WB053703

         to now be equipment described as:

         One (1) Calumet Coach Company Model MMT-481P Siemens ECAT Mobile Pet
         Unit, VIN #1TKH04220WB053702

II.      LOCATION: Lessee and Lessor agree to cause the equipment location
         described as:

         2240 Shelter Island Drive, San Diego County, San Diego, CA

         to now be the equipment location described as:

         207 N. LYNDON LANE, LOUISVILLE, KY 40222 EXCEPT WHEN BEING USED BY
         LESSEE IN THE COURSE OF ITS BUSINESS.

The undersigned agree to all the terms and conditions set forth above and IN
WITNESS WHEREOF, Lessor and Lessee hereby execute this Amendment this ____ day
of ___________, 2000.

FINOVA CAPITAL CORPORATION                MOBILE PET SYSTEMS, INC.
--------------------------                ------------------------
Lessor                                    Lessee

By:                                       By: /s/ Paul Crowe          CEO
   -----------------------                   -----------------------------
            Title                                                    Title

<PAGE>

LEASE SCHEDULE                                       FINOVA CAPITAL CORPORATION
No. 4125.03A                                         311 SOUTH WACKER DRIVE
                                                     SUITE 4400
                                                     CHICAGO, ILLINOIS 60606

    The following described equipment and accessories are leased by Lessor to
    Lessee, on the terms specified in this Lease Schedule, subject to the
    terms and conditions of the Equipment Lease Number 4125 dated April 8,
    1999.

--------------------------------------------------------------------------------
1.  DESCRIPTION OF EQUIPMENT: One (1) Calumet Coach Company Model
    MMT-481P SIEMENS ECAT Mobile Pet Unit, VIN #1TKH04222WB053703

--------------------------------------------------------------------------------

2.  SELLER:             Calumet Coach Company
                        -------------------------------------------------------
    SELLER'S ADDRESS:   2150 East Dolton Road, Calumet City, IL 60409
                        -------------------------------------------------------

--------------------------------------------------------------------------------
3.  TERM:               60 MONTHS             4.  SECURITY DEPOSIT:   N/A
                        -------------------                       --------------

5.  RENTAL PAYMENTS: $2,645.27 per period for three (3) consecutive monthly
rental periods, followed by $3,637.25 per period for the next three (3)
consecutive monthly rental periods; followed by $6,062.64 per period for the
remaining fifty four (54) consecutive rental periods.
    To each rental payment, when paid, shall be added the amount of any
applicable sales or use tax.

6.  ADVANCE RENTALS:  $ 2,645.27  to be applied to the  FIRST  rental payments.
                        ---------                      -------
--------------------------------------------------------------------------------

7.  EQUIPMENT LOCATION:  2240 Shelter Island Drive        San Diego
                         -----------------------------------------------------
                          (Street)                         (City)

                         San Diego                           CA
                         -----------------------------------------------------
                          (County)                         (State)

8.  LESSEE'S ADDRESS (if different than paragraph 7 above):

------------------------------------------------------------------------------
      (Street)         (City)          (State)          (Zip Code)

--------------------------------------------------------------------------------
9.  Other Provisions

-  "Notwithstanding anything to the contrary in Equipment lease F4125 and
    provided Lessee is not in default thereunder, Lessee, upon giving Lessor
    ninety (90) days prior written notice, shall have a one time Option to
    Purchase not less than all the Equipment under this Lease at maturity of
    the base lease term for the then fair market value not to exceed twelve
    percent (12.00%) of the original equipment cost a paid by Lessor the
    Equipment and any other items or charges included in the Lease plus
    applicable sales taxes."

-   FINOVA has the option to adjust its monthly payment consistent with
    increases in the five-year, fixed-rate cost of financing from the date of
    this Lease Schedule to delivery and acceptance of the Equipment. Upon
    acceptance of the Equipment, the monthly payment will become fixed for the
    entire term.
--------------------------------------------------------------------------------

The parties hereto have executed this Lease Schedule as of the 17th day of
March, 2000.

FINOVA CAPITAL CORPORATION                    MOBILE PET SYSTEMS, INC.
--------------------------                    --------------------------
Lessor                                         Lessee

By:                                       By:  /s/ Paul Crowe, CEO
    ------------------------------            ------------------------------
                   Title                                       Title

<PAGE>

                              AMENDMENT NUMBER ONE
                                       TO
                           LEASE SCHEDULE NO. 4125.03B
                                     BETWEEN
                      FINOVA CAPITAL CORPORATION ("LESSOR")
                                       AND
                       MOBILE PET SYSTEMS, INC. ("LESSEE")

I.       LOCATION: Lessee and Lessor agree to cause the equipment location
         described as:

         2240 Shelter Island Drive, San Diego County, San Diego, CA

         to now be the equipment location described as:

         207 N. Lyndon Lane, Louisville, KY 40222 except when being used by
         Lessee in the course of its business.

The undersigned agree to all the terms and conditions set forth above and IN
WITNESS WHEREOF, Lessor and Lessee hereby execute this Amendment this ________
day of ______ _______________, 2000.

FINOVA CAPITAL CORPORATION                    MOBILE PET SYSTEMS, INC.
--------------------------                    ------------------------
Lessor                                        Lessee

By:                                           By:   /s/ Paul Crowe         CEO
    ----------------------                       -------------------------------
             Title                                                        Title

(R0383)

<PAGE>

LEASE SCHEDULE                                       FINOVA CAPITAL CORPORATION
No. 4125.03B                                         311 SOUTH WACKER DRIVE
                                                     SUITE 4400
                                                     CHICAGO, ILLINOIS 60606

    The following described equipment and accessories are leased by Lessor to
    Lessee, on the terms specified in this Lease Schedule, subject to the
    terms and conditions of the Equipment Lease Number 4125 dated April 8,
    1999.

--------------------------------------------------------------------------------
1.  DESCRIPTION OF EQUIPMENT: One (1) Siemens ECAT EXACT P.E.T. Scanner
    System as further itemized on the Equipment Schedule Addendum No. One
    attached hereto and made a part hereof.

--------------------------------------------------------------------------------

2.  SELLER:             Siemens Medical Systems, Inc.
                        -------------------------------------------------------
    SELLER'S ADDRESS:   186 Wood Avenue South, Iselin, NJ 08830
                        -------------------------------------------------------

--------------------------------------------------------------------------------
3.  TERM:               60 MONTHS              4.  SECURITY DEPOSIT:    N/A
                      -------------------                            -----------

5.  RENTAL PAYMENTS: $13,354.73 per period for the three (3) consecutive
monthly rental periods, followed by $18,362.75 per period for the next three
(3) consecutive monthly rental periods; followed by $30,607.36 per period for
the remaining fifty four (54) consecutive rental periods.

    To each rental payment, when paid, shall be added the amount of any
applicable sales or use tax.

6.  ADVANCE RENTALS:  $ 13,354.73  to be applied to the  FIRST  rental payments.
                        ---------                      -------
--------------------------------------------------------------------------------

7.  EQUIPMENT LOCATION:  2240 Shelter Island Drive, Suite 110       San Diego
                         -----------------------------------------------------
                          (Street)                                   (City)

                         San Diego                           CA
                         -----------------------------------------------------
                          (County)                         (State)

8.  LESSEE'S ADDRESS (if different than paragraph 7 above):

------------------------------------------------------------------------------
      (Street)         (City)          (State)          (Zip Code)

--------------------------------------------------------------------------------
9.  Other Provisions

-   Addendum No. One attached hereon and made a part hereof.

-  "Notwithstanding anything to the contrary in Equipment lease F4125 and
    provided Lessee is not in default thereunder, Lessee, upon giving Lessor
    ninety (90) days prior written notice, shall have a one time Option to
    Purchase not less than all the Equipment under this Lease at maturity of
    the base lease term for the then fair market value not to exceed twelve
    percent (12.00%) of the original equipment cost as paid by Lessor the
    Equipment and any other items or charges included in the Lease plus
    applicable sales taxes."

-   FINOVA has the option to adjust its monthly payment consistent with
    increases in the five-year, fixed-rate cost of financing from the date of
    this Lease Schedule to delivery and acceptance of the Equipment. Upon
    acceptance of the Equipment, the monthly payment will become fixed for the
    entire term.
--------------------------------------------------------------------------------

The parties hereto have executed this Lease Schedule as of the 17th day of
March, 2000.

FINOVA CAPITAL CORPORATION                    MOBILE PET SYSTEMS, INC.
--------------------------                    ------------------------------
Lessor                                         Lessee

By:                                           By: /s/ Paul Crowe, CEO
    ------------------------------            ------------------------------
                   Title                                       Title

<PAGE>

                               ADDENDUM NO. ONE
                                      TO
                         LEASE SCHEDULE NO. 4125.03B
                                   BETWEEN
                       FINOVA CAPITAL CORPORATION (LESSOR)
                                      AND
                        MOBILE PET SYSTEMS, INC. (LESSEE)

                        DATED THE 17TH DAY OF MARCH, 2000

                               EQUIPMENT SCHEDULE

ONE (1) SIEMENS ECAT EXACT P.E.T. SCANNER SYSTEM

The ECAT EXACT is a high-resolution positron emission tomography system for
imaging biochemical processes and metabolism for whole body applications. The
multi-detector ring system provides 3D acquisition and reconstruction in the
static and dynamic modes.

The ECAT EXACT consists of a 47 image plane system with a 16.2 cm (6.4 in)
field of view.

     High spatial slice resolution in transaxial and axial dimensions
     Three-dimensional display of organs with a large axial view
     Excellent volume sensitivity
     Fast acquisition and reconstruction of 64 x 64 and 128 x 128 matrices
     High-resolution, flicker free, color display monitor
     Unique block detector technology provides excellent temporal and energy
resolution response
     Simultaneous data acquisition and image reconstruction for high patient
throughput
     Retractable rotating rod source holders for quick and accurate
attenuation correction. (Ge-68 is available in safe, solid form from
recommended vendors)
     Water-cooled gentry for quiet operation
     Window-oriented operating software

The system consists of:

Whole Body Ring Detector Gantry:
     824 mm detector ring diameter
     56.2 cm gantry aperture
     16.2 cm (6.4 inch) axial field of view
     Nine laser lines for precise, reproducible patient positioning
     Dual operator controls on gantry for positioning from either side of
patient
     Count rate monitor at gantry control panels
     Three integrated retractable transmission rod source holders which
extend/retract from a lead housing under computer control for enhanced
patient throughput and reduced radiation exposure

Patient Handling System:
     Low attenuation foam core carbon fiber pallet
     57 to 93 cm (22 to 36 inch) vertical motion range
     195 cm (77 inch) horizontal scan range
     Low attenuation head holder
     Maximum patient weight of 159 kg (350 lbs)

Data Acquisition/Processing and Storage Electronics:
     Image plane coincidence processor
     Real-time sorter (RTS) with 64 MB memory
     VME Bus acquisition controller
     1 Quad 1860 array processor
     SCSI (small computer system interface) adapter to the VME Bus
     18.0 GB Acquisition disk
     Ethernet interface to operator's console

                                       1

<PAGE>

                               ADDENDUM NO. ONE
                                      TO
                         LEASE SCHEDULE NO. 4125.03B
                                   BETWEEN
                       FINOVA CAPITAL CORPORATION (LESSOR)
                                      AND
                        MOBILE PET SYSTEMS, INC. (LESSEE)

                         DATED THE 17TH DAY OF MARCH, 2000

                               EQUIPMENT SCHEDULE

     Sparc processor

Operator's Console for Image Display and Analysis:
     UltraSPARC 60 with dual 450MHz CPUs
     1.0 GB main memory
     1 x 18.0 GB, 1 x 9.0 GB Internal disk storage
     2.6 GB erasable optical storage system for archiving image data
     CD ROM drive (mounted in desktop storage unit)
     600 dpi laser printer
     Ethernet connection to data acquisition/processing and storage electronics
     4mm DAT (digital audio tape) archive system, mounted in desktop storage
unit
     UNIX operating system and utilities
     TCP/IP and network file system communication software
     Floppy drive
     20 in. Color monitor
     ECAT Software version 7.2 features, including iterative reconstruction,
segmented attenuation correction, and the whole body protocol

ECAT STANDARD SOFTWARE
Image Acquisition:
     Transmission scan allows accurate measurement of tissue attenuation
correction coefficients
     Static emission scan
     Dynamic emission scan
     Acquisition protocols
     Image reconstruction and processing
     Wide variety of reconstruction filters
     Image size and displacement parameters
     Calculated or measured attenuation correction

Display Software:
     Window-oriented to allow simultaneous acquisition, reconstruction, data
processing and image display
     Image zoom and magnification
     Multi-image static display
     Any oblique data re-orientation
     Cine mode display
     Multiple plane dynamic displays
     Region of interest and image profiles
     Image filtering, summing and arithmetic
     Regions of interest and image statistics
     Screen save/restore operations
     Image labeling with variable fonts and graphics
     Interactive color translation table operations
     Three-dimensional volume interactive data review (transverse, sagittal and
coronal displays)

Utilities Software:
     Patient database

                                       2

<PAGE>

                               ADDENDUM NO. ONE
                                      TO
                         LEASE SCHEDULE NO. 4125.03B
                                   BETWEEN
                       FINOVA CAPITAL CORPORATION (LESSOR)
                                      AND
                        MOBILE PET SYSTEMS, INC. (LESSEE)

                        DATED THE 17TH DAY OF MARCH, 2000

                               EQUIPMENT SCHEDULE

     Patient data archive
     Motion control
     System calibration
     System normalization
     Performance tests
     System diagnostics

Educational Software:
     Multi-media educational package LPP (Let's Play PET) for use on separate
Macintosh or ICON (not provided with system)

Systems Documentation (1 set):
     ECAT scanner software manual
     ECAT scanner hardware manual

     Water-cooled, whole-body gantry
     9216 Bismuth germanate (BGO) crystals
     16.2 cm (6.4 inch) axial field of view
     Simultaneous acquisition of up to 47 contiguous slices
     23 Interplane retractable septa for high axial resolution, high
sensitivity, and minimum scatter to permit 3-D acquisition
     Full-body patient couch and head holder
     Data acquisition and electronics
     ECAT Software
     Operators console and peripherals

PRE-INSTALL KIT EXACT

ULTRASPARC REMOTE WORKSTATION

UltraSPARC console workstation for 7.2 systems
Includes the following or better:
         UltraSPARC 60 450 MHz
         1.0 GB RAM
         1 x 18.0 GB, 1 x 9.0 GB disk
         20" monitor
         CD drive
         Floppy drive
         ECAT software version 7.2
         IDL 5.0 runtime license

ERASABLE OPTICAL DISK

Additional 2.6 GB erasable optical disk drive for storing data and images at an
UltraSPARC Remote Workstation. Remote Workstation option required for purchase
of this option

ISOLATION TRANSFORMER (US)

                                       3

<PAGE>

Transformer for isolating ECAT power from line power

GANTRY AIR/WATER CHILLER (60HZ)

Closed system air/water chiller. Requires onsite chilled water. Requires
siting in well-ventilated utility room.

PET APPLICATIONS TRAINING (PER DAY)

Operator's training for ECAT Scanners performed by applications specialist.
Scheduling for training is available upon request. A quantity of 3 days is
recommended for upgrades to 7.1 software. A quantity of 5 days is recommended
for new scanner installations.

EXACT SOURCES KIT (1ST FILLING)

Calibration and transmission sources for the ECAT EXACT. These sources are to be
purchased with a new ECAT EXACT scanner order. Sources consist of the following:

         1 Set of Rods
         1 CS-20-1 Uniform Phantom
         1 CS-20-3 Uniform Phantom
         1 LS-LA Set-up Source
         2 Phantom Shields

ECAT CODONICS PRINTER

ECAT Codonics medical diagnostic imager configuration including dye
diffusion/direct thermal dual mode color and grayscale output. Configuration
comes equipped with dye diffusion ribbon. 8.5 x 11 paper (100 sheets) and tray
and 8 x 10 clear base file (100 sheets) and tray. Also includes postscript and
DICOM support. Hardware provided for network connection to ECAT network.

ECAT EXACT MOBILE OPTION

Includes all of the items necessary for a mobile coach or trailer installation
         6.0 KVA UPS
         Documentation and manuals specific for mobile environments
         Bed stations for transport
         Modified phantom shields

ERASABLE OPTICAL DISK

Additional 2.6 GB erasable optical disk drive for storing data and images at an
UltraSPARC Remote Workstation. Remote Workstation option required for purchase
of this option.

ULTRASPARC REMOTE WORKSTATION

UltraSPARC console workstation for 7.2 systems

                                       4

<PAGE>

Includes the following or better:

         UltraSPARC 60 450 MHz
         1.0 GB RAM
         1 x 18.0 GB, 1 x 9.0 GB disk
         20" monitor
         CD drive
         Floppy drive
         ECAT software version 7.2
         IDL 5.0 runtime license

NU SYS MISC MATL UPS

FINOVA CAPITAL CORPORATION                    MOBILE PET SYSTEMS, INC.
----------------------------------            ------------------------------
Lessor                                         Lessee

By:                                           By: /s/  Paul Crowe,  CEO
    ------------------------------            ------------------------------
                   Title                                       Title

                                       5
<PAGE>

                               ADDENDUM NO. ONE
                                      TO
                         LEASE SCHEDULE NO. 4125.03B
                                   BETWEEN
                       FINOVA CAPITAL CORPORATION (LESSOR)
                                      AND
                        MOBILE PET SYSTEMS, INC. (LESSEE)

                        DATED THE 17TH DAY OF MARCH, 2000

                               EQUIPMENT SCHEDULE

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