I've got ahold an old iMac (CRT, 600mhz). It had system 9 on it, so i whiped it and installed Tiger. The display has been acting strangely. It periodically shifts to one side, untill part of the display has moved off the visible part of the screen. Its almost as if I have the "Displays" system preference open and am playing with the "geometry" tab. Has anyone experienced anything like this? I've tried the basics. Firmware is up to date, and i've reset the PM unit, nvram, etc.