You do not have to purchase every program for every machine with Win XP. It depends on the license, but XP itself doesn't care. XP does care if you install the same copy of XP on another machine though. I used to use Win 2K, and no serious problems except for finding that half of my programs didn't work anymore. I didn't lock up much, maybe just 1 or 2 lockups a day. I have found that XP hasn't locked up on me since I bought it when it came out. And, as a bonus, every program I have tried with the exception of PBooost has worked including the ones that wouldn't under Win2K. PBoost does work somewhat, it just doesn't work at the same time as Poser because of the file system. That would be true most likely with Win2K also. Although my experience has been that XP Pro is the best OS from Microsoft, your mileage may vary.