Did you know that if you have an 64-bit Athlon chip (or an Opteron server in your closet), you can download XP-64? It's a "customer preview program" but not a closed beta. You're going to want to do this in a dual-boot configuration with a 32-bit OS: although the Windows-on-Windows 64-32 emulation layer (WoW64) works in many cases, it doesn't work with .NET CLR's 1.0 or 1.1 or VS.NET 2003.