XP Pro......been using steady for over a year.....rebooted once (the XP equivalent of a crash). No more "blue screens" like you'll get in any Win 9x system. Defrag it once a month and you won't crash at all. You can leave it running for months without having to restart your computer. The memory management is amazing. I have a 1.7 ghz processor, 512 mb of ram and P-IV. I run Bryce 4, Vue 4.1+, the new PsP 8 and Poser 5(not to mention all the typical Microsoft Office stuff I use for my job). Poser 5 is the only real memory hog in the batch, but XP Pro manages the memory issues without shutting down a thing.....simply allocates more memory so Poser can finish whatever it's doing. I'll never own anothe OS.