I've had this problem in the past and am encountering it again now.

The problem is as follows:

1) Fresh installation of Windows 98 SE.
2) Screen resolution changed from default of 640x480 with 256 colours to
800x600 with 24-bit colours.
3) Restart the computer.
4) Resolution has returned to 640x480 with 256 colours.

If you set the resolution at 800x600 with 24-bit colours then 'shut down'
the workstation, then turn it on again, the resolution is fine. It only
seems to reset when you 'reboot'.

I have tried 3 different graphics cards in the machine and they all have the
same effect. Albeit they are the same model graphics card.

Has anyone encountered this before? If so do you have any advice or a
workaround?

Thanks :-)