I had this same question and eventually found the answer.
The image file needed is X17-48538.img available from the Microsoft OEM site.
It contains:
- readme.txt 2/26/2011 1204
- windows6.1-KB976902-X86-Wave0.cab 2/26/2011 4532924
- windows6.1-KB976902-X86-Wave1.cab 2/26/2011 4531728
- windows6.1-KB976932-X86-Wave0.cab 2/26/2011 354704066
- windows6.1-KB976932-X86-Wave1.cab 2/26/2011 541001258
You should be able to get it through your OEM if you don't have direct access to the MyOEM site.