<PAGE>   1
                                                                   Exhibit 10.51


                   CAMBRIDGE ENERGY RESEARCH ASSOCIATES, INC.
                                DEMAND TERM NOTE

                                                               February 11, 1998


            Cambridge Energy Research Associates, Inc., a Massachusetts
corporation (the "Company"), for value received, hereby promises to pay on
demand (subject to the limitations set forth below) and from time to time to
McCarthy, Crisanti & Maffei, Inc., a New York corporation ("MCM" or the
"Lender"), the principal amount of twenty-six million four hundred thousand U.S.
dollars ($26,400,000), with interest. Payments of principal and interest shall
be payable as set forth below, and made in lawful money of the United States of
America to such account as the Lender shall designate from time to time.
Capitalized terms not otherwise defined herein shall have the same meaning
ascribed thereto in the Credit Agreement, dated as of February 12, 1998, among
MCM, as Borrower, Global Decisions Group LLC (the "Parent"), as Guarantor, Bank
of America N.T. & S.A., as Documentation Agent, and The Chase Manhattan Bank, as
Administrative Agent, (the "Credit Agreement").

1. Payments of Principal. The Company shall repay the principal hereof, in whole
or in part, upon the demand of the Lender; provided, however, that (i) no demand
shall be made by the Lender until five (5) days have elapsed from the date
hereof and (ii) the Lender shall not demand payment and the Company shall not be
obligated to repay any principal hereunder prior to June 30, 2000, unless any
demand for payment by the Lender is authorized by the Board of Directors of the
Parent (the "Board").

 2. Final Maturity. Notwithstanding anything contained herein, this Note shall
mature and all outstanding principal and interest shall be paid by the Company
to the Lender on February 1, 2008.

3. Payment of Interest. Interest will accrue on the outstanding principal amount
of this Note and unpaid interest thereon at a rate equal to the rate
attributable from time to time to the Term Notes under the Credit Agreement. All
interest shall be payable quarterly, in arrears, on the Interest Payment Dates,
provided, however, that (i) no demand shall be made by the Lender until five (5)
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days have elapsed from the date hereof and (ii) interest shall accrue but shall
not be paid by the Company prior to June 30, 2000, unless such payment is
demanded by the Lender upon authorization by the Board. Interest on unpaid
principal and interest shall accrue and compound quarterly from the date hereof
until all obligations hereunder are repaid in full by the Company.
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4. Security. This Note is entitled to the benefits of collateral granted to the
Lender by the Company pursuant to the Collateral Agreement (the "CERA Collateral
Agreement"), dated February 11, 1998, between the Lender and the Company and the
Trademark Security Agreement (the "CERA Trademark Security Agreement"), dated
February 11, 1998 between the Lender and the Company (the CERA Collateral
Agreement and the CERA Trademark Security Agreement, collectively, the "CERA
Security Agreements").

5. Events of Default. The principal amount of this Note and all accrued but
unpaid interest thereon shall become immediately due and payable upon the
occurrence of any of the following events (each, an "Event of Default"):

                        (a) upon notice from the Lender, if the Company shall
            default in the payment of principal or interest on this Note when
            due, as provided in Sections 1 and 2 hereof or a default of the
            covenant contained herein; or

                        (b) (i) the Company shall commence any case, proceeding
            or other action (A) under any existing or future law of any
            jurisdiction, domestic or foreign, relating to bankruptcy,
            insolvency, reorganization or relief of debtors, seeking to have an
            order for relief entered with respect to it, or seeking to
            adjudicate it a bankrupt or insolvent, or seeking reorganization,
            arrangement, adjustment, winding-up, liquidation, dissolution,
            composition or other relief with respect to it or its debts, or (B)
            seeking appointment of a receiver, trustee, custodian, conservator
            or other similar official for it or for all or any substantial part
            of its assets, or the Company shall make a general assignment for
            the benefit of its creditors; or (ii) there shall be commenced
            against the Company any case, proceeding or other action of a nature
            referred to in clause (i) above which (A) results in the entry or an
            order for relief or any such adjudication or appointment or (B)
            remains undismissed, undischarged, unstayed or unbonded for a period
            of 60 days; or (iii) there shall be commenced against the Company
            any case, proceeding or other action seeking issuance of a warrant
            of attachment, execution, distraint or similar process against all
            or any substantial part of its assets which results in the entry of
            an order for any such relief which shall not have been vacated,
            discharged, stayed or bonded pending appeal within 60 days from the
            entry thereof; (iv) the Company shall take any corporate action in
            furtherance of, or indicating its consent to, approval of, or
            acquiescence in, any of the acts set forth in clause (i), (ii) or
            (iii) above; or (v) the Company shall be generally unable to, or
            shall admit in writing its general 
<PAGE>   4
            inability to, pay its debts as they become due.

                        (c) There shall have been an Event of Default under the
Revolving Credit Note, dated the date hereof, made by the Company to the Lender
(the "Revolving Note"); or

                        (d) There shall have been a Default under Section 9 of
the Credit Agreement and the Loans thereunder shall have been declared due and
payable;

Upon any of the circumstances described in paragraphs 5(b) or 5(d), all unpaid
principal and interest (including interest thereon) of this Note shall
automatically and immediately become due.

6. Representations and Warranties of the Company. To induce the Lender to make
the loan evidenced hereby, the Company hereby represents and warrants to the
Lender that:

                        (a)  The audited balance sheets of the Company as of 
June 30, 1995, 1996 and 1997 and the audited statements of earnings, statements
of shareholders' equity and statements of cash flows for the years ended June
30, 1995, 1996, and 1997 have heretofore been furnished to the Lender. The
unaudited interim financial statements of the Company for the three-month period
ended September 30, 1997, have heretofore been furnished to the Lender. Such
financial statements (including the notes thereto) in the case of the financial
statements described in the first sentence of this section (i) have been audited
by KPMG Peat Marwick LLP, (ii) except in the case of unaudited financial
statements described in the second sentence of this section, for the absence of
footnotes, have been prepared in accordance with GAAP consistently applied
throughout the periods covered thereby and (iii) present fairly, in all material
respects, the financial condition, results of operations and cash flows of the
Company as of such dates and for such periods (except for normal year-end audit
adjustments). During the period from June 30, 1997 to and including the date
hereof, except as provided in the Transaction Documents, there has been no sale,
transfer or other disposition by the Company, and no purchase or other
acquisition by it of any business or property (including any Capital Stock of
any other Person) material in relation to the financial condition of the Company
which is not reflected in the foregoing financial statements or in the 
<PAGE>   5
notes thereto or has not otherwise been disclosed in a writing to the Lender on
or prior to the date hereof.

                        (b) As of the date hereof, after giving effect to the
consummation of the Transactions, the Company is Solvent.

                        (c) The Company (i) is duly incorporated or organized,
validly existing and in good standing under the laws of the jurisdiction of its
incorporation, (ii) has the corporate power and authority, and the legal right,
to own and operate its property, to lease the property it operates as lessee and
to conduct the business in which it is currently engaged, except to the extent
that the failure to have such power and authority or legal right would not be
reasonably expected to have a material adverse effect on the business, assets,
operations, property, condition (financial or otherwise) or prospects of the
Company, (a "Material Adverse Effect"), (iii) is duly qualified as a foreign
corporation and in good standing under the laws of each jurisdiction where its
ownership, lease or operation of property or the conduct of its business
requires such qualification, other than in such jurisdictions where the failure
to be so qualified and in good standing would not be reasonably expected to have
a Material Adverse Effect and (iv) is in compliance with All Requirements of
Law, except to the extent that the failure to comply therewith would not, in the
aggregate, be reasonably expected to have Material Adverse Effect.

                        (d) The Company has the corporate power and authority,
and the legal right, to make, deliver and perform under this Note and the
Transaction Documents, to obtain extensions of credit hereunder and under the
Revolving Note (this note and the Revolving Note, collectively, the "Notes") and
has taken all necessary corporate action to authorize the execution, delivery
and performance of the Notes and the Transaction Documents and to authorize the
extensions of credit on the terms and conditions contained in the Notes. No
consent or authorization of, filing with, notice to or other similar act by or
in respect of, any Governmental Authority or any other Person is required to be
obtained or made by or on behalf of the Company in connection with the
execution, delivery, performance, validity or enforceability of the Transaction
Documents or with the extensions of credit under the Notes, except for (i)
consents, authorizations, notices and filings required to be obtained or made on
or prior to the date hereof and described in Schedule 1, all of which, unless
noted in Schedule 1, have been obtained or made on or prior to the Effective
Date, (ii) filings to perfect the Liens created by the CERA Security Agreements,
(iii) filings pursuant to the Assignment of Claims Act of 1940, as amended (31
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U.S.C. Section 3727 et seq.), in respect of Accounts Receivable of the Company
the obligor in respect of which is the United States of America or any
department, agency or instrumentality thereof and (iv) consents, authorizations,
notices and filings which the failure to obtain or make which would reasonably
be expected to have a Material Adverse Effect. This Note has been duly executed
and delivered by the Company and the Transaction Documents have been or will be
duly executed and delivered on behalf of the Company. This Note constitutes a
legal, valid and binding obligation of the Company and each Transaction
Document, as executed and delivered does constitute, or when executed and
delivered, will constitute, a legal, valid and binding obligation of the
Company, enforceable against the Company in accordance with its terms, except as
enforceability may be limited by applicable bankruptcy, insolvency,
reorganization, moratorium or similar laws affecting the enforcement of
creditors' rights generally and by general equitable principles (whether
enforcement is sought by proceedings in equity or law).

                        (e) The execution, delivery and performance of the Notes
and the Transaction Documents by the Company, the extensions of credit hereunder
and the use of the proceeds thereof (i) will not violate any Requirement of Law
or Contractual Obligation of the Company in any respect that would reasonably be
expected to have a Material Adverse Effect and (ii) will not result in, or
require, the creation or imposition of any Lien (other than the Liens permitted
by the CERA Collateral Agreement) on any of its properties or revenues pursuant
to any such Requirement of Law or Contractual Obligation.

                        (f) No litigation, investigation or proceeding of or
before any arbitrator or Governmental Authority is pending or, to the knowledge
of the Company, threatened by or against the Company or against any of its
properties or revenues (i) which is so pending or threatened at any time on or
prior to the date hereof and relates to the Notes, the CERA Security Agreements,
the Transaction Documents or any of the transactions contemplated hereby or
thereby or (ii) which would reasonably be expected to have a Material Adverse
Effect.

                        (g) The Company is not in default under or with respect
to any of its Contractual Obligations in any respect which would be reasonably
expected to have a Material Adverse Effect. No Event of Default has occurred and
is continuing.
<PAGE>   7
                        (h) The Company has good record and marketable title in
fee simple to, or a valid leasehold interest in, all its material real property,
and good title to, or a valid leasehold interest in, all its other material
property other than any failure to have such title to or interest in such
property that would not reasonably be expected to have a Material Adverse
Effect, and none of such property is subject to any Lien, except for Liens
permitted by the CERA Collateral Agreement.

                        (i) The Company owns, or has the legal right to use, all
United States trademarks, trademark applications, tradenames, copyrights,
technology, know-how and processes necessary for it to conduct its business as
currently conducted (the "Intellectual Property") except for those the failure
to own or have such legal right to use would not be reasonably expected to have
a Material Adverse Effect. No claim has been asserted and is pending by any
Person challenging or questioning the use of any such Intellectual Property or
the validity or effectiveness of any such Intellectual Property, nor does the
Company know of such claim, and, to the knowledge of the Company, the use of
such Intellectual Property by the Company does not infringe on the rights of any
Person, except for claims and infringements which in the aggregate, would not
reasonably be expected to have a Material Adverse Effect.

                        (j)  No Requirement of Law or Contractual Obligation of 
the Company would be reasonably expected to have a Material Adverse Effect.

                        (k) The Company has filed or caused to be filed all
United States federal income tax returns and all other material tax returns
which are required to be filed and has paid (i) all taxes shown to be due and
payable on such returns and (ii) all taxes shown to be due and payable on any
assessments of which it has received notice made against it or any of its
property and all other taxes, fees or other charges imposed on it or any of its
property by any Governmental Authority, and no tax Lien has been filed, and no
claim is being asserted, with respect to any such tax, fee or other charge
(other than any (A) taxes, fees or other charges with respect to which the
failure to pay, in the aggregate, would not have a Material Adverse Effect or
(B) taxes, fees or other charges in the amount or validity of which are
currently being contested in good faith by appropriate proceedings diligently
conducted and with respect to reserves in conformity with GAAP have ben provided
on the books of the Company).

                        (l) No part of the proceeds of the extensions of credit
under the Notes will be used for any purpose which violates the provisions of
the 
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Regulations of the Board, including, without limitation, Regulation G,
Regulation T or Regulation X of the Board. 

                        (m) During the five year period prior to the date
hereof, with respect to any Plan (or, with respect to (vi) or (viii) below, as
of the date such representation is made or deemed made), none of the following
events or conditions, either individually or in the aggregate, has resulted or
is reasonably likely to result in a Material Adverse Effect: (i) the occurrence
of a Reportable Event; (ii) the occurrence of an "accumulated funding
deficiency" (within the meaning of Section 412 of the Code or Section 302 of
ERISA); (iii) the occurrence of any noncompliance with the applicable provisions
of ERISA or the Code; (iv) a termination of a Single Employer Plan (other than a
standard termination pursuant to Section 4041(b) of ERISA); (v) the creation of
a Lien on the property of the Company in favor of the PBGC or a Plan; (vi) the
existence of any Underfunding with respect to any Single Employer Plan; (vii)
the occurrence of a complete or partial withdrawal from any Multiemployer Plan
by the Company or any Commonly Controlled Entity; (viii) the incurrence of any
liability by the Company or any Commonly Controlled Entity under ERISA if, as a
result of the withdrawal by the Company or any such Commonly Controlled Entity
from any Multiemployer Plans as of the annual valuation date most closely
preceding the date on which this representation is made or deemed made; or (ix)
the Reorganization or Insolvency of any Multiemployer Plan. There have been no
transactions that resulted or could result in any liability to the Company or
any Commonly Controlled Entity under Section 4069 or ERISA or Section 4212(c) of
ERISA.

                        (n) Except with respect to (i) Liens on equipment
constituting fixtures, (ii) any reserved rights of the United States government
as required under law, (iii) Liens upon Trademarks and Trademark Licenses (as
such terms are defined in the Guarantee and Collateral Agreement) to the extent
that (A) such Liens are not otherwise perfected by the filing of financing
statements under the Uniform Commercial Code or by the filing and acceptance
thereof in the United States and Trademark Office or (B) such Trademarks and
Trademark Licenses are not, individually or in the aggregate, material to the
business of the Company, (iv) Liens on uncertificated securities, (v) Liens on
collateral the perfection of which requires filings in or other actions under
the laws of jurisdictions outside of the United States of America, any State,
territory or dependency thereof or the District of Columbia (except to the
extent that such filings or other actions have been made or taken), (vi) Liens
on contracts or Accounts Receivable on which the United States of America or any
department, 
<PAGE>   9
agency, or instrumentality thereof is the obligor, (vii) Liens on Proceeds of
Accounts Receivable, until transferred to or deposited in the Collateral
Proceeds Account (if any), and (viii) claims of creditors of Persons receiving
goods included as Collateral for "sale or return" within the meaning of Section
2-326 of the Uniform Commercial Code of the applicable jurisdiction, upon filing
of the financing statements delivered to the Lender by the Company on the date
hereof in the jurisdictions listed on Schedule 2 hereto (which financing
statements are in proper form for filing in such jurisdictions) (and the
recording of the CERA Trademark Security Agreement in the PTO and the making of
filings after the date hereof in any other jurisdiction as may be necessary
under any Requirement of Law) and the delivery to, and continuing possession by,
the Lender of all Instruments, Chattel Paper, Investment Property and Documents
a security interest in which is or may be perfected by possession, the Liens
created pursuant to the CERA Collateral Agreement, when executed and delivered,
will constitute valid Liens on and, to the extent provided therein, perfected
security interests in the collateral referred to in such CERA Security
Agreements (but as to the Copyrights and the Copyright Licenses (as defined in
the CERA Collateral Agreement) and accounts arising therefrom, only to the
extent the Uniform Commercial Code of the relevant jurisdiction, from time to
time in effect, is applicable) in favor of the Lender, which Liens will be prior
to all other Liens of all other Persons, except for Liens permitted pursuant to
the CERA Collateral Agreement, and which Liens are enforceable as such as
against all other Persons (except, with respect to goods only, buyers in the
ordinary course of business to the extent provided in Section 9-307(1) of the
Uniform Commercial Code as from time to time in effect in the applicable
jurisdiction and except to the extent that recording of an assignment or other
transfer of title to the Lender in the United States Patent and Trademark Office
may be necessary for such enforceability), except as enforceability may be
limited by applicable bankruptcy, insolvency, reorganization, moratorium or
similar laws affecting the enforcement of creditors' rights generally and by
general equitable principles (whether enforcement is sought by proceedings in
equity or at law). Notwithstanding any other provision of this Note, capitalized
terms which are used in this subsection (j) and not defined in this Note or the
Credit Agreement are so used as defined in the CERA Collateral Agreement.

                        (o) Other than exceptions to any of the following that
would not, individually or in the aggregate, reasonably be expected to give rise
to a Material Adverse Effect:

                        (1) The Company: (i) is, and within the period of all
            applicable 
<PAGE>   10
            statutes of limitation has been, in compliance with all applicable
            Environmental Laws and (ii) holds all Environmental Permits (each of
            which is in full force and effect) required for any of their current
            operations or for any property owned, leased, or otherwise operated
            by it and reasonably expects to timely obtain without material
            expense all such Environmental Permits required for planned
            operations

                        (2) Materials of Environmental Concern have not been
            transported, disposed of, emitted, discharged, or otherwise released
            or threatened to be released, to or at any real property presently
            or formerly owned, leased or operated by the Company or at any other
            location, which could reasonably be expected to (i) give rise to
            liability of the Company under any applicable Environmental Law or
            (ii) impair the fair saleable value of any real property owned by
            the Company.

                        (3) The Company has not received any written request for
            information, or been notified that it is a potentially responsible
            party, under the federal Comprehensive Environmental Response,
            Compensation, and Liability Act or any similar Environmental Law, or
            received any other written request for information
            with respect to any Materials of Environmental Concern.

                         (4) The Company has not entered into or agreed to any
            consent decree, order or settlement or other agreement, nor is
            subject to any judgment, decree, or order or other agreement, in any
            judicial, administrative, arbitral or other forum, relating to
            compliance with or liability under any Environmental Law.

                        (p) The written information, reports, financial
statements, exhibits and schedules furnished by or on behalf of the Company to
the Lender in connection with the Transactions or this Note, taken as a whole,
did not contain as of the date hereof any material misstatement of fact. It is
understood that (x) no representation or warranty is made concerning the
forecasts, estimates, pro forma information, projections and statements as to
anticipated future performance or conditions, and the assumptions on which they
were based, contained in any such information, reports, financial statements,
exhibits or schedules, except that as of the date such forecasts, estimates, pro
forma information, projections and statements were generated, (1) such
forecasts, estimates, pro forma information, projections and statements were
based on the good faith assumptions of the management of the Company and (2)
such 
<PAGE>   11
forecasts, estimates, pro forma information, projections and statements, and the
assumptions on which they were based, may or may not prove to be correct.

7. Covenant. The Company shall not, and shall not permit any of its Subsidiaries
(if any) to, take any action that would result in a violation of any of the
covenants of the Lender contained in the Credit Agreement.

8. Transfer. This Note is a registered Note and is transferable only upon
surrender of this Note for registration of transfer, duly endorsed, or
accompanied by a written instrument of transfer duly executed, by the Lender or
its attorney duly authorized in writing. References in this Note to the "Lender"
shall mean the person in whose name this Note is at the time registered on the
register kept by the Company, and the Company may treat such person as the owner
of this Note for the purpose of receiving payment and for all other purposes.

9. No Modification or Waiver; Successors and Assigns. This Note may not be
changed, modified or discharged orally, nor may any waivers or consents be given
orally hereunder, and every such change, modification, discharge, waiver or
consent shall be in writing, duly signed by or on behalf of the Company and
Lender. This Note shall be binding upon and shall inure to the benefit of the
Company and the Lender and their respective successors and assigns.

10. GOVERNING LAW. THIS NOTE SHALL BE GOVERNED BY THE LAWS OF THE STATE OF NEW
YORK, WITHOUT REGARD TO ITS PRINCIPLES OF CONFLICTS OF LAWS.

11. Notices. All notices, requests and other communications required or
permitted to be given under this Note shall be deemed to have been duly given if
(a) personally delivered, (b) mailed, certified or registered mail with postage
prepaid, (c) sent by next day or overnight mail or delivery or (d) sent by fax
as follows:

                        (i)         If to the Company to it at:

                                    20 University Road
                                    Cambridge, Massachusetts 02138
                                    Attention:  President

                        (ii)        If to the Lender to it at:
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                                    One Chase Manhattan Plaza, 37th Floor
                                    New York, New York 10005
                                    Attention:  Mr. David D. Nixon


                        (iii)       If to any assignee of the Lender pursuant to
                                    paragraph 6 hereof, to such address that
                                    such assignee provides to the Company upon
                                    surrender for transfer of this Note.




                        CAMBRIDGE ENERGY RESEARCH ASSOCIATES, INC.


                                           By:__________________________
                                           Name:
                                           Title:
<PAGE>   13
ANNEX A



<TABLE>
<CAPTION>
                Date                  Prepayment               Princ. Balance             Notation Made By
<S>                                   <C>                      <C>                        <C> 
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</TABLE>