yea its a driver option
in any profile, or global if you want, select advanced options, and there will be an option for transparency AA, with options of None, Multisample, Supersample
multisample does a great job and requires much less power than Supersample, so it leaves more of the GPUs power for the game itself.
i use multisample and the fences in CS:S on the de_nuke level looked awesome.