I'm with ya Bigun I still have a 500mhz machine that runs like a top other than in a few areas like multitasking and multimedia, but I'm still running 98SE on mine.
If you put in a music CD do you have the same performance problem?
Tee's right. Getting rid of the 64mb and replacing it with one that matches your other will help. There is a few tricks that will help your music play better, but really its an issue of the combination of your CPU and OS. Windows 2000 is far more resource hungry that your 98 was, and unless your CPU(processor) is a MMX(
MMX technology is designed to accelerate multimedia and communications applications) its going to struggle running most modern multimedia.
Trick one: If you have a favorite play list you could re-sample your songs from 44khz(CD quality) to 16khz(radio quality). Of course you loose some quality but if you music stutters anyway it could be an improvement. There is lots of free software that can be used to re-sample songs.
Trick two: A long forgotten trick to squeeze more speed out of a PC is a RamDrive. The performance issue your having is partly due to the speed of your hard drive. Reading music from your drive to memory then Music Match takes a lot of processor power. You can free up your processor by putting your songs in memory ahead of time allowing it to concentrate more on playing the music.
Setting up a ramdrive in the old Windows was pretty easy because it was a far more common practice 10 years ago, but it still can be done in W2k its just a bit more complicated. Here is a good link explaining how to setup and ramdrive in W2k, but as I said its pretty intense.
http://cyberwizardpit.net/article3.htm
Once you have a ramdrive setup you can copy not only music but any files(documents, movies) to this drive and they will run much faster.
As you can see there is no real simple answer other than upgrading the old PC.