Win98SE, 512MB RAM, P3-667 platform.

After operating for a while, suddenly things start to go wacky. For instance,
fonts in Win message boxes change. Or I go to save an Excel spreadsheet and I
get a "not enough resources" message, which is sometimes truncated due
presumably to ... not enough resources.

On boot-up, Eudora is the only task electively started. A Ctrl-Alt-Del shows
the following other running tasks:

Explorer
Rundll32
Stimon
Systray

If I initialise SystemMonitor, it indicates about 213MB of RAM as allocated when
nothing (else) is running. 50 kernel threads, processor 50% now with Agent
running (otherwise this would be somewhat lower). Swapfile size 50MB. Locked
memory 143MB.

If I remove Eudora from the startup process, the figures look a tad better but
not dramatically so.

Have done a virus scan and all reports clean.

Machine is networked using DHCP via a NAT router.

Can anyone suggest what else to look at/for in finding the underlying cause?