Well, it's a totally different operating system, and the way it works with software and hardware is a lot more efficent. You'll see a lot less instability (which includes memory leaks) in Windows 2000/XP. When you upgrade from ME to XP, you don't "fix" anything, you install a new OS. Underneath the user interface, ME and XP aren't a thing alike in terms of handling resources and memory, etc. etc. So when you "upgrade" you really aren't upgrading. They're totally different at the core.