I agree with KarlC about Vista vs XP. But keep in mind that Microsoft has a scheduled date of 4/14/2009 for an End of Life on XP, meaning they will no longer support it or sell it. Currently the EOL for businesses is 2014, but home users at that time will be apparently out of luck.

There is a movement to extend the EOL date for all users until Vista is more stable and Microsoft is "considering" it.

Back to Vista! On top of the increased hardware requirements to run Vista, there is Vista Service Pack 1 which is about half a gig is size! Can you say Giant Bug Fix? Add to that, poor driver support, (drivers for older printers and other devices), and you have all the requirements for total frustration.