Mdd -
mdd, also known as ManTech dd or Memory dd, is a command line program to acquire an image of the memory of a running Windows computer. The program has been included in the Helix incident response tool.
Status
The current version of mdd (mdd_1.3.exe) runs on Window XP to SP3 and Vista to SP 2, and may run on other versions.
The driver uses the Physical Memory Object Memory Imaging Mehod and returns a file handle to a user-mode program via an IOCTL on the device file named:
\\.\memdd 
Once the file handle has been returned the driver and associated memdd device is no longer required and can be removed, which is what the mdd utility does.
Building from source
Load the x64 Free Build Environment from the WDK (in start menu)
Go to the mdd directory, e.g. C:\src\mdd\driver\mdd\ and run build
You should now have mdd.sys in C:\src\mdd\driver\mdd\objfre_win7_amd64\amd64
Signing the driver
Make sure the WDK is installed, you need that for the signing.
Get the right cross certificate file, see Cross-Certificates for Kernel Mode Code Signing
Convert the key you have to pfx, if its cert + key you want:
setup a secure spot to put the private key, this should not be on corp or unprotected at any time
openssl pkcs12 -export -out out.pfx -inkey in.key -in in.crt -certfile ca.crt 
use a strong password
shred the .key immediately after use
Sign the driver by running:
signTool sign /v /ac <crosscertificatefile> /f <pathtopfx> /p <pfx password> /t http://timestamp.verisign.com/scripts/timestamp.dll <driver.sys> 
Also see: SignTool
Usage
To execute mdd, you must start cmd.exe. The options are:
-o filename - required to actually run mdd
-w - license information
-v - verbose
To run mdd, the account you are using must have administrator access to the machine you wish to image (however, it does not have to be the Administrator account; it only needs to be in the local Administrator group). The program works by installing a service, called mdd, although see below for problems.
Known Issues
These are the known problems with mdd.
Error 1073
This is a Windows Service Manager error. mdd executes by registering itself as a service, so it can run as administrator, although this does not mean you can run mdd without having administrator access. At the end of a normal execution, the service is deleted. However, mdd can accidentally leave the service installed, and this prevents further imaging. This could be caused by the system crashing (or an intentional system crash) during imaging, or by attempting to stop the imaging with control-c. If this happens, a knowledgeable Windows user will open up the Services tab in Computer Manager, but unfortunately, Windows has a wonderful feature that allows services, when they are registered, to state whether or not they wish to be seen in the Service Manager. This amazing concept allows services to run less visibly, and should be considered a class-a security flaw. Fortunately, there's a way around this, using the command line (cmd.exe).
Run cmd.exe
In cmd.exe, run "sc help" to see the service manager command line tool
Run "sc query" to see all of the currently registered services, but note that this list will overflow the default line buffer of cmd.exe (this is adjustable, but not necessary for our purposes)
Run "sc query mdd" and - ta-da - you'll see the mdd service
Run "sc delete mdd" and it's gone, and mdd can now be run again.
Error 1062
John Judd will be entering text here.
In Vista, even if you are in the administrator group, you do not necessarily run programs with administrator access (this is actually a major improvement to the security model of Windows). You can start programs, including cmd.exe, with admin privileges, but in this case, that won't help. You will not be able to image to a Network Share from Vista. There is no known workaround. This problem may exist in Windows 7.