I've reinstalled twice now and added
mat_aaquality "0"
mat_antialias "2"
to my config

That's all the advice I can find from reading a couple pages of the forum.

Anything else I can do/try?

mat_antialias "2"

Try 0.

You could also try and disable windows aero theme manually by right clicking your hl2.exe, (in your css folder) properties, compatibility and check disable desktop composition and disable desktop themes.

Just seen you have vista.

Dont try and fix it and get windows 7 :P

I like your desktop.

Just played a game on 0, didn't work either.

Can't find disable desktop composition, but then again nor can I find the compatibility tab :D Windows Vista remember!

I know, I was forced to format a while ago and after doing-so discovered my XP disc is AWOL ._.

& thanks Rob :D

right click your hl2.exe in your css folder,
It will be somewhere like, C:/programfiles/steam/steamapps/username/counterstrikesource,
then click properties, then compatibility.

Im sure vista uses windows aero aswell :(

annoying, right clicked it this time and now it has the tab ._.

also upgrading to win7. maybe this'll fix it at least

edit; fixed