Microsoft Knowledge Base Article 326687 contains the following SYMPTOMS:
When you upgrade your computer to Windows XP, you may receive an error message that is similar to one of the following:
C0000221 (Bad Image Checksum)
STOP: C0000221 - Bad Image Checksum in ModuleName
STOP: C0000221 - Bad Image Checksum. User32.dll is possibly corrupt. The header check sum does not match the computed check sum.