Dell D420 with occasional screen freeze

[pal8]

The screen freeze on a Dell D420 with Ubuntu 8.10. Often with a distorted screen with horizontal lines. What could be wrong? I suspect it's something with the graphic card and driver. How can I check what driver I use and how can I re-install or update it?

[pal8]

Very strange, but it seems to be related to the Firewall. It happened 3 times when I used Firestarter. I removed it and installed another firewall program. When using that same thing happened again.