IMac :: G5 Terminal Display - Red Symbols Overlay Desktop?

I think my 20" G5 iMac ( the model before the integrated iSight) may have what amounts to a terminal graphic card problem. It was working perfectly until suddenly an odd red pattern made up of what looks oddly like thousands of tiny i-ching symbols overlayed over the actual desktop. I have tried rebooting from the CD which suggests it isn't a software issue, and since I understand the graphics card is part of the logic board, it's probably not worth replacing it financially.