Hi,

it seems the Matrox cards are a little bit sensitive to the 
environment in general. You might try a lower AGP speed (1x). Be 
shure to have the latest Bios. And as allways, have a good power 
supply.

I had a K7M with G400 and a T-Bird 700 running X without 
problems for some time, so it should not be a problem per se. I 
used an Enermax PS, a good ventilated case, Global Win heatsink 
with YS Tech fans and Tennmax heatsink/fan combos for the 
northbridge and G400. This might be overkill, but I fear the heat ;), 
but even my Performa lost some of its problems when I put a 
heatsink and thermal tape to the 68040.

HTH

mike