If you have not already upgraded to Windows 7, here’s why you want to do it.
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This post in PC World
gives you a good summary of the reasons to switch.
I switched a year ago and am glad I did. Windows 7 is more stable than XP.
The Taskbar is a dramatic improvement in the way you access your apps and, as the post notes, using libraries to segregate documents from videos and music is a time saver.