Thanks Philipp of NT Compatible who tells us that his compatibility database at NT Compatible has been updated for both Windows XP 64 Bit and Windows Server 2003 64 Bit versions.
This database is featuring user submitted compatibility results and tips for applications, games, and hardware running under Windows NT 4.0, Windows 2000, Windows XP, Windows Server 2003, and now Windows XP/Windows Server 2003 (64 Bit)
Its a great resource and was unequaled in delivering information for compatibility issues on the then new Windows 2000 a few years back. The database has grown since then to be a trustworthy and accurate resource for NT core operating systems.