Diamond V770 resolution problems

I have:
DFI K6BV3+ MB
w/ a AMD K6-2 450Mhz
128MB RAM
multiple HD's
AWE64 Value
Diamond V770 Video card
and a Compaq 1425 14" Monitor.

The problem I have is that the resolution I want is 800x600. When I use the standard files it works fine. As soon as I load up a game though the screen changes resolution to 640x480 and becomes unusable. I have installed the newest drivers, and have contacted Diamond to no avail. I have to reboot every time I play a game, it is driving me nuts!!!
Does anyone know a solution to this?

I have seen that before with the TNT2 cards. I belive it is caused by the 14 inch monitor. I tested it here an an old 14" Socos monitor and the same thing happens. Make sure you have your monitor defined correctly in the control panel. But I have only seen it with 14 inch monitors. Another solution may be to try the detonator drivers off the Nvidia site. However, you are using an excellent graphics card and an older, small monitor. I would actually say it is time for a new one.