Well, if oyu would give us your comp's technical specs so we can tell whether you comp is just crappy and tell you in detail how to fix things in whatever OS you have.

Basically, if the step doesn't work, go onto the next:

1. Reinstall the copy of DirectX that's on your RTW CD.

2. Reinstall your graphics card drivers.

3. Set your graphic's card's acceleration to 0.

4. Alt+ Ctrl+ Del shutdown all the extra background programs you don't need running.

5. Run Disk Defrag(helps prevent crashes and speeds things up a tiny bit), Adaware, etc

6. Get a new computer.