Here is the link to the newly released app compatibility guide for XP SP2:

http://www.microsoft.com/downloads/details.aspx?FamilyId=9300BECF-2DEE-4772-ADD9-AD0EAF89C4A7&displaylang=en

Here is the link where information on the beta for ACT 4.0 will show up.  If you are and ISV or build applications running on XP, ACT is a necessary evil.

http://www.microsoft.com/windows/appcompatibility/act4.mspx