That last point from JG is a good one. I've heard it from more than one authoritative source - including MS themselves at one of their TechNet briefs - that if your PC is used a lot you should do a clean reinstall annually to clean out the Registry rubbish and "wrong" versions of DLLs etc. I keep putting off the moment and will now wait for a winter's day; but I know that the Registry of my busiest PC (NT4) is now about 10 MB compared with about 4 MB for a new installation. Most of the rubbish is legacy stuff and fragments from programs loaded temporarily and then deleted.
It is often said that Win 95/98 should be rebooted once a day and Win NT(WS) every few days or so just to clean out the RAM. If you do this, you may avoid random crashes.