*edit: i posted before i even looked at the picture. stupid me. turn off truform (im almost sure thats the name but i honestly cant remember, its the one under or above vertical sync). its under opengl properties in advanced display settings
step 1:
turn off 4 x AA, test for same problem.
still not fixed?
step 2:
turn off 8 x AIF, test for same problem.
still not fixed?
Reinstall drivers to latest, if that doesnt work, find older version drivers, if that doesnt work try an alternative driver (in the case of ATI, omega drivers)
and finally, reinstall HL