I am using a 4890 Video card on my mac pro 1,1 and recently upgraded to 10.6.4... I was reluctant to upgrade because when i originally upgraded to 10.6.3 I would always have issues with random screen scrambling. So, at that time, I revert back to my SL disc 10.6. The actual 10.6.4 upgrade was cake, no hacks needed, just needed to install netkas' program and restart. Unfortunately, the screen scrambling is back. This time when the computer sits for longer than 10 minutes, which forces me to reset the machine... I've turned off all sleeping and standby options hoping that was the issue, no luck. Anyone else have this problem? I've attached a picture of what it looks like. This isn't my actual computer but this is the same thing that happens.