So that the next person doesn't have to struggle with this like I did...
How to get the Matrox G550 working with an nForce2 board....
Your comment about AGP & the errors I saw from startx got me thinking that I was looking in the wrong place. So I looked at /etc/X11/XF86Config-4. Sure enough, when I commented out the line:
Option "AGPMode" "4"
and changed the lines (2 head card, so there were two lines in my file):
it worked! For some odd reason, it appears I have to switch to a text console and back to the X (Alt-F7) screen before I see anything, but otherwise, it appears everything works, and you were right, I didn't need AGP.
thanks for your help,