My desktop from Nov 2007 started to have issues running XP last year. Kept crashing, stalling, hanging...
I reformatted the drive and installed Win7 Professional on it. Now, it runs like new again without any issues. Reasonably quick too, despite its age.
Now my laptop with Vista is starting to get fussy, so it may soon be facing the same treatment.
Can't help but wonder if Microsoft introduces some problems in updates just to encourage people to upgrade. Or maybe it's just years and years of updates that makes the system get cludgie.