Andrea:

If you really can't resist the new features of XP OS, but you would like to keep your music (and possibly other) applications functional, my sugestion is to split your hard disk in two partitions. This is, of course, easier if your hard is a reasonably sized one. In one of them you install your brand new OS, and all the applications which already have apropriate drivers, and in your old Win 98/Millenium partition, you install all your music stuff. Later, as new drivers /new versions of some programs are developed for the new OS, you may "move" then to your new "XP partition".
An example of a (comercial) easy-to-use program that resizes/splits your hard disk in different partitions is "Partition Magic", but there are other free utilities that perform the same job (with less flexibility).

E-mail me if my "dialect" sounds strange or if you need further detail.

JP Matias.