Known issues with G5 NVidia 6800
We received a report that this card, needed for 30 inch monitors, does not support the standard bitmap font Blender uses by default.
You can bypass that by setting the UI to use antialiased fonts, which looks much better anyway. This is an option in the "user menu", part of the "Info Window" in blender; just pull down the top header to reveil this menu and set the "Internation Fonts" option.
You can make such settings become default by saving it with the CTRL+U command. Please note this saves the entire GUI as it is, including objects, materials, etc.