[Mobhack]

I have no idea then what's up with your setup.

As a last gasp - try turning your sound off,
- in the game options launcher misc tab, set the mouse interface interface click off
- in the game preferences screen, turn both of the sounds off (Battle FX and Sound FX).

Why? - well some users have reported that having sound on makes unit movement and firing animations jerky. Seems to be a sound card related issue. Worth a try to see if that is what is affecting you.