I'm thinking there's something wrong with 2D stuff on Radeon X series cards.
I'm using a Radeon Mobility X1400 myself, and I'm experiencing the following issues:
1. The game locks up when trying to open any menu (Tab, J, M, Esc)
2. My framerate drops from "actually very playable" to "this would be slow even for a slideshow" if I enable the postprocessing effects (as others have said, image trail is probably the culprit, but I haven't tested them individually yet)
3. The intro logos and loading screen seem to be doing
some weird tiled repetition thing.
Those are all related to 2D processing, no?
The tiling thing makes me wonder if the game is somehow misreading the screen resolution (I've tried using 640x480, 800x600, and 1024x768 in fullscreen) on these cards...