Failed video on new install of suse 6.4

I have w2k and mandrake 8.1 installed, but I wanted
1. to have a distribution that supports jbuilder5 personal
2. try out SuSe which I'd never installed

The problem:
upon booting suse tried to feed a video signal beyond my monitor's abilities.

This also happened last week when I tried to install RH 6.2.

Question:
How can I modify the boot video mode?

Video card: Matrox G450 currently running at 67.5kHz / 75 Hz 1152x864 in
Mandrake.

Thanks.