This is an issue with the map Battle Of Yavin if you have an NVIDIA card and are using Windows Vista. The issue is to do with Alpha Channels (which make things transparent) being
There is one way to fix it, which is by pressing Alt-Tab then coming back into game. So long as you do not press Alt or T, the map shouldn't go all iffy. If it doesn't work once, try it again and it should do the trick.
Time to spend some bucks. Upgrade your video card driver or if you have one then time to upgrade to higher one. If you have PCI express 16 or 2.0 slot you can get a G force one under $50 may be. TG and Best Buy has some great deals.