Mac Pro 1,1 OSX 10.6.8 corrupted display
It seems that you're seeing two problems simultaneously: video corruption and a software error returned by your antivirus application. This suggests that the system has possible hardware issues. I would boot the system to the Apple Hardware Test and run diagnostics to see whether there is a hardware failure. Video corruption is often traceable to a bad GPU and/or bad RAM. Since you replaced the video card, the bad GPU is unlikely.

If AHT returns errors, you may wish to take the system into a Genius Bar or authorized Apple repair centre for further evaluation. If not, you may have a transient issue. You can try swapping around/removing RAM to determine if one or more of your SO-DIMMs have gone bad.