It depends on what you are doing with your computer. I have 3 OS's on my system. Windows ME, Windows 2000 and Linux. I do what I can in Linux, do everything else in Windows 2000 and then play my games in ME.
XP is hype! Microsoft claims XP will be the best OS ever. But people define the best in so many different ways. If all you are doing is e-mail and browsing the web...get 98/ME. If you are doing gaming and video editing and stuff...get ME. For productivity get Windows 2000 and if you want networking and superior reliability...Linux.
XP is supposed to be based on the Windows NT Kernel combined with the compatibility of ME (which means it won't be much different than 2000). The Windows 9x/ME and Dos kernel are being scrapped by Microsoft. XP is not geared towards gaming; it is geared towards media and multimedia. If you want a gaming OS...ME or 98se is your best bet as of today.
As of right now, I don't plan on upgrading. I just don't need an OS like XP. And in my opimion it is not some major must-have upgrade. I can do everything I ever wanted to do with my computer right now. This is not a must have upgrade that Microsoft is claiming. If you have 2000 and ME dual booted...you basically already have XP. Because that is all it is.