Can you give us more info, Hoplite?

What settings are you playing on? vh/vh, m/m?
Are you using anthing other than default settings on your video options?

Are you using the patched version of M2TW or the original release?

What is your PC running for an operating system, what's your memory size, have you got anything running in the background while you're playing the game? etc.

Some of our real Guild pros might have run into your problem before.