I am literally having this problem as we speak. It had been working fine until I built a water treatment plant. From there, I started getting garbled images including incorrectly rendered buildings, roads with extra lines, and a variety of other graphical mishaps. I thought maybe it was just that city, but even in other cities in my region, I began having that problem.
To problem solve, I went through my plugins folder and removed the last thing I downloaded, but that didn't help. I've quit the game and restarted my computer twice already. I tried the 32-bit z option when loading the game...all to no avail.
I'm running a MacBook Pro 2.26 Intel Core 2 Duo with 2 GB of memory and the NVIDIA GeForce 9400M @ 256 MB VRAM using OS X 10.6.3. Any help would be greatly appreciated!
EDIT to make changes to spelling...apparently I can't type this morning .