I have the same problem that Todd has i have an Nvidia Geforce 6200 256 mb and some faces of the structures have that problem. I'll put an example:
http://img226.imageshack.us/my.php?image=ejemplope3.png
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"If the doors of perception were cleansed every thing would appear to man as it is, infinite. For man has closed himself up, till he sees all things thru' narrow chinks of his cavern." -- William Blake