17" imac display problem

[egghead3]

Hi

Im a YDL newbie and a newbie to linux in general. I just installed YDL on my 1ghz 17" imac G4. Installation went smoothly but my display settings are clearly not correct. Despite selecting both the 17" imac monitor and the proper video card, I can only view a square section in the middle of the screen. About 1" is cut off the top and the bottom and about 2" on each side leaving only black bars.

Does anyone have any suggestions?

Thanks
Greg