I had very few glitches with my 1950XT in FEAR, certain papers and such, the textures got all scrambled. Thought it was just an ati/driver issue.
In hl, i know there are some issues with AA and HDR. Not sure if HDR was in hl2, but as i recall the 1st version with hdr (ep1?) has issues with aa+hdr. Turn one of these off, it may solve the problem.