Now what I wonder, is how it's gonna run on 64 bit XP...I'll freepmail ya if your interested...
I can help you out here too: it ain't going to run on the WinXP 64-bit edition. Valve hasn't added the code into the game. The only game I can think of with a 64-bit edition pending is Unreal Tournament 2004, and that isn't coming out until the final XP 64-bit edition comes out, which isn't happening until sometime next year.
Valve's already started on episodic content for HL2, so maybe we'll see a 64-bit edition available over Steam sometime.