That's a kernel panic which is usually caused by a hardware problem. Disconnect all non-needed periphials and see if that resolves the problem. Did you recently upgrade the computer, i.e., add ram?
You should run the Apple Hadware Test found on your install disk to see if that kicks anything out.
Edit:
The anomalies on the picture may indicate a bad or failing GPU as well. If you cannot boot into the AHT, you may need to call apple