I own Photoshop 6.0 and use it regularly on Windows XP. I've also spent some time with someone else's Photoshop CS2 (the latest version), and could see little real improvement. It has a new heal brush, and a prettier interface, which is nice, but it mostly it just seemed to be big, slow, & forever to launch.

I'm sticking with 6.0 on my machine. There isn't $150 worth of improvement in CS2, and it works perfectly with XP.