QB used to require you to go no more than 2 Versions before an Upgrade. If you had a product and tried to use a new version of QB that was 3 or more versions newer than the one you where using you had to buy a License for an Interim version install it upgrade your Data File and then move it to the finial version that you wanted to use and upgrade within 2 new versions from then on.
I believe that Quick Books has done away with the requirement now.
As for which OS is better I would say XP. As already stated Vista has lots of known compatibility Issues so just changing OS's to Vista will most likely render lots of existing hardware like Scanners/ Printers/Web Cams and so on unusable.
If you are starting from Scratch with all new hardware Vista is OK but it's expensive to do things like that in Offices as it is unlikely that all of the hardware reaches it's end of Lifetime at the same time so you have to dispose of existing working Hardware just to use the new OS. If you are using hardware released within the past 5 or so years they should work with XP but they may not work with Vista and most unlikely to work with 7. Even some things like Web Cams and Video Capture Cards that are Vista Compatible do not work with 7.
If you need to retain your existing hardware have you tried reloading the 2000 Boxes with a Clean Install of Y2K? If it;s been running for this long and is now slow that is because the OS has picked up so much junk that it's being slowed down. A wipe and reinstall will cure that. ;)
Col
