Slowly, slowly, Windows 2000 is being assigned to the scrapheap of obsolescence. More and more progam upgrades are no longer able to run on this venerable OS, the most notable (for me) being the Canon photo suite and as of today, Zone Alarm.
I have upgraded a two of my computers to XP over the past year to accomodate these changes; I may do another. It's a shame I have to make this change. I like Windows 2000, it's been the OS I've used for the past six years or so, and it has done everything I needed it to up until now. There's little in XP that's any better; it's not faster and is more of a memory hog. (Vista I will skip entirely, too many horror stories and my own experience reveals it to be bloatware of the most bloated kind.)
As I have a hardware firewall and some very old computers that act as little more than file servers, I'll probably keep Windows 2000 running on those. It does the job. Linux is also an option here. But I have become fond of 2000, it is wonderfully stable and reliable. Even in coming years, I might keep it running on one machine for old time's sake.