Cannot get to 1024x768, 16M colours

Hi everybody,

I've been given an old machine (PIII-500) to reinstall for a friend.

So far, I've installed Windows '98 Second Edition on the machine, but I
cannot seem to get the resolution of the screen to go up to 1024x768 at 16
million colours.

At the display settings screen, I can choose the resolution, and I've added
a Super VGA screen (standard driver), but whatever choice I make, it
defaults back to 640x480, 16 colours.

Now I know for a fact that the video card in the machine is an old Matrox
one, so I started fiddling around with some of the more popular Matrox
drivers, but to no avail.

As this is a second-hand machine, no driver CDs are available in any form,
so I'm down to my own collection of drivers, the Windows CD, and whatever
the Net seems to offer.

Is there anybody who can tell me how to get this resolution to my desired
settings?

Thanks,

Ikke