Earlier today, AMD released Catalyst 12.10 and Catalyst 12.11 Beta. It appears that both drivers don't support Windows XP. In fact, XP isn't even listed in the Catalyst 12.10
release notes. This could be a strong indication that AMD is planning to discontinue monthly driver support for Windows XP. This won't be a surprise as some hot upcoming PC games (Black Ops II, Hitman Absolution) and even software (Photoshop CS7) won't support Windows XP either.
We sent an email to AMD with a link to this article asking for a clarification on this matter. We will update this story as soon when we hear back from them.