Dude how old is your computer? Windows 98 isn't a supported platform for recent hardware and that is probably why you "cannot see" your Nvidia Graphics card and other hardware.
If you already have your own genuine Windows XP serial, then why don't you borrow a windows xp CD/DVD form someone and reinstall that, Windows 98 will not work properly with hardware that is less than 5 years old at least.
Failing that, Windows 7 is in Release Canidate 1 at the moment and is free to use for a certain period of time (I think RC1 keys will work up until June 2010) so go grab a copy of it here: http://www.microsoft.com/windows/windows-7/
Hope this helps