A friend of mine that works in the IT industry just stunned me by asking whether there was anything new in SP2 for Windows XP - seems we haven't quite got the message out there enough yet - be prepared for this one, it is not just another Service Pack.
So, for him and you, I've linked the Microsoft.com page that conveniently lists the resources available for SP2 for IT Pros:
Developer-focused info is here: http://msdn.microsoft.com/security/productinfo/xpsp2/default.aspx
I don't care what anyone else tells you - in my opinion, this is Windows XP - The Second Coming. It's a pretty major product upgrade, and you need to have at least a rough idea of what's happening in it if your professional life intersects with it.