XP rocks
A zillion places to find XP, correct as previous posts indicate, you can still buy it from somewhere
Let's look ahead 3-5 years though...
-Windows next OS will be twice as big as Vista ME and with Solid State Drives becoming the norm, this will be the only way to speed up boot times and performance
-Mac still a niche market for those with money
-Linux ubuntu/next decent windows manager product is ok but the power of linux is still reserved for those who know how to use commands
XP I'm afraid was MS last decent OS.
With new exploits coming out that affect all current OS/browsers and wi-fi, a revolutionary change is required on how we interface with the internet and each other.
Enjoy it while you can.