Run Setup from the DVD, and create an installation package. Set the target folder to be somewhere that your SCCM server can access - I used a folder in a share where I store all my SCCM packages.
Then you need to create a package based on that folder. The package will need to contain several programs which will install the prerequisite software (including updates) and then GP, then any GP updates.
The install of Dexterity/DrWatson/SQL components is different for x64/x86 so I'll deal with x64, and note the differences for x86.
I set all the programs to run hidden, and whether or not a user is logged in and assign to targeted machines (and in the Accounts PC build task sequence)
Dexterity for x64 clients:
msiexec /i DexteritySharedComponents\Microsoft_Dexterity11_SharedComponents_x64_en-us.msi /qn
NOTE - there's a different MSI for x86.
Latest Dexterity Update: (you may have a different update of course)
msiexec /update DexteritySharedComponents\Microsoft_Dexterity11_SharedComponents-KB2435568-ENU.msp /qn
Dr. Watson for Dexterity x64
msiexec /i Watson\dw20sharedamd64.msi APPGUID={F5459EB2-A662-4EB3-AD94-E771DC2F542A} /qn /norestart
NOTE - the APPGUID for x86 is {74C84D32-0BFE-4DF1-A59A-49EEECE4043B}, and the msi is dw20shared.msi
SQL Native Client x64
msiexec.exe /i SqlNativeClient\sqlncli_x64.msi /qn
NOTE - the msi is different for x86
Open XML SDK 2.0
msiexec.exe /i OpenXmlFormatSDK\OpenXMLSDKv2.msi /qn
Lync 2010 SDK
MSIExec.exe /i LyncSdkRedist\LyncSdkRedist.msi /qn
Dynamics GP 2010 - finally!!!! :)
msiexec /i GreatPlains.msi /qn
Dynamics GP 2010 Update (whichever MSP you're up to)
msiexec.exe /update Updates\MicrosoftDynamicsGP11-KB2682502-ENU.msp /qn
Then create a task sequence (I have one for x64, one for x86) that does the install in the order above.
Hope this helps and isn't too late for you!
Neil