Windows desktop (XP, Vista or Win7) EC2 AMI for QA testing
Solution 1:
I would suspect the answer will be no, because Amazon S3 has to use SPLA licensing for their windows installs and Desktop OS's are not available on SPLA. I would suggest some sort of local virtualisation and an MSDN licence.
Solution 2:
Bit late to this, but google 'hens teeth cross browser' they provide community Windows AMIs but only in US east region.