Windows ME is basically Windows 98 with some bits bolted on (in the same way that win98 is win95 with bits bolted on). Basically all that offers over win 98 is that it makes it easier to create a local network at home.
Windows 2000 is NT4 with some added fuctionality, such as allowing plug and play devices.
But to answer the question, ME is really only worth getting if you want to network computers at home, otherwise hold on to win98 for the time being. Unless you can get a copy for free, of course.