SC3K Graphics Problem

I'm running the game on windows xp, and it runs fine. however, when I
scroll the map around the city graphics won't load. instead i get
light blue squares in place of my city's buildings. If I zoom out, the
graphics load up. But as soon as I scroll again I get the same
problem. I've tried lowering the screen resolution and reducing the
sound effects and traffic/sim effects but it dosn't help. Oh my
machine is a 3ghz 512ram, btw.

Anyone have any suggestions on what I can do to resolve this? I havn't
been able to find anything on the web.

Thanks,
-T