Microsoft Technet is a great tool for solving problems with MS software. I know I wouldn't be able to live without it in my job. Although I subscribe to the CD version you can get the same thing from http://technet.microsoft.com
What I would do...
1) Upgrade to the latest OS. (if possible)
2) Run windows update to get the latest patches (http://windowsupdate.microsoft.com
3) Run a spyware checker (http://security.kolla.de
4) Run a good virus scanner (http://www.grisoft.com
5) Run a good firewall (http://www.sygate.com
6) Your systray should have no more then 3 or 4 programs (Virus scanner, firewall, IM, and popup filter) running in it.
7) Check over your startup config and stop unneeded programs with msconfig (http://www.pacs-portal.co.uk/startup_content.htm
to determin what it is you're stopping). Things like MS Office Tool, real audio player, quicktime, etc... are NOT needed to run at startup, get rid of them.
8) Your desktop should have no more then 10 icons on it.
9) Your background pic should be no larger then 50k.
10) Uninstall any programs (using add/remove programs) that you do not use. Don't be a pack rat, if you've used it once and keep it around just because, get rid of it.
11) Run an OS repair (Can't remember if 98 has that or not).
Everything I mentioned above can and will help speed up your machine and stop it from GPFing. Most registry problems and BSOD/GPF problems come from a compatibility problem in the registry or with updated dlls. Keeping your system clean and tidy will help keep it running as smoothly as possible.