Video Problem - Screen Flicker

[eapplen]

I'm having this problem when too many units appear on the screen, buildings and units flicker on and off (the forests do this too, so I'm guessing it's all the objects besides the backgrounds). When there AREN'T that many units, it works just fine. I updated to the newest Detonator drivers (I'm using a GeForce 4), and DirectX9a.

Any suggestions? HELP!