You should be able to, as long as you know what actual folder your "music library" is stored in. Check that it is a folder somewhere on your PC other than in a Creative directory.
If you want to be doubly sure and have enough spare hard drive space, make another copy of that folder with all your mp3s to an entirely different place on your computer, and call it something totally different, so that if for some reason the re-install wipes things, then you've got them all saved anyway. (That's in addition to having them on your player, if you're only talking about software, not having to reinstall the firmware on your player as well.)
But from memory I've intsalled an updated version of mediasource before with no problems...
