From my memory of my last Mesh there should be a page in your computer manual telling you how to reformat. It isn't particularly easy but it is ok to do if you follow the instructions exactly and patiently. You will need the disc of drivers that came with your machine plus the windows disc that would, I guess, be supplied with machines at that time. If you don't have these, don't bother.
I think USB 2 does not work on windows 98 but others will be able to tell you
Windows xp probably will work but not fast
I wouldn't start on graphics cards personally being more inclined to save for a new computer