Not that I'm a full-fledged techie or nothin' like that (although I occasionally play one on TV), the fact that it works for a while and then goes bad leads me to think about memory links, general degradation, and things like that. Have you considered....
1. Shutting down all extra background programs before running W&W? Could be something is hanging around back there as the real source of the problem. In particular, things like virus scanners and such can be a problem.
2. Defragging your hard drive. Could be something related to good ol' hardware thrashing.
3. Check your virtual memory settings. If you've got 256MB of memory, something in the neighborhood of 768MB of virtual is not unreasonable.
4. You do have sufficient disk space, don't you? Swapping to a nearly full disk is never good for performance of any kind...
5. What version of Win98? You might check for patches and upgrades related to memory, video, or performance. Poor video might only be the symptom; the root cause may be elsewhere.
Anyway, some thoughts that can at least occupy you for a little bit
