Well, it turned out one has to do some nasty trick to get X up: after entering startx, all output is delivered to the second monitor port on the Matrox G450 card, so you have to hot-swap your monitor (if you're working in single-head mode like me) to get X up and running. Dual-head has same "feature": run startx, and after that plug in the second monitor. Warning: monitor on second connector (=only monitor in single-head) is known as first monitor to the card (might be important if you have 2 different types).
matrox has a forum: forum.matrox.com/cgi-bin/mgaforum/ Go ask the matrox-developers to change this, 'cause it's totally ridiculuous ;-) -- It's not whether you win or lose, it's how you place the blame.
