P.S. Notice Windows 2003 ain't in that 1st list, it's the same as 2000 in that aspect
Yeah WGA doesn't apply to Windows Server 2003 and XP Pro x64 Edition, don't know why, but XP Pro x64 is based on Server 2003 so that's why it won't work on XP x64.
I seem to remember seeing Genuine Advantage in a bundle of M$ updates.
For XP, WGA is update KB905474 and is downloaded as a "critical update" so it downloads automatically when updating Windows. Sneaky I think, as far as I'm concerned, WGA is not "cirtical" to anybody but Microsoft. The average user won't care if their copy of Windows is genuine or not, only Microsoft will. I'm not advocating piracy by saying this, I'm saying it's only an "advantage" to Microsoft and rather a "disadvantage" to everybody else who has to put up with it.
Basically from day 1 the machine had issues - it would freeze, reboot, crash with IRQL_NOT_LESS_OR_EQUAL and a number of such nice things. I will never know if it was faulty hardware, or some hardware/OS incompatibility
IRQL_NOT_LESS_OR_EQUAL often points to bad drivers, usually graphics drivers or SATA controllers or things like that.