Spotted this one via nvnews. Apparently Half-Life will have compatibility problems with FSAA support & certain Graphics cards (Seemingly everything that's not an ATi Radeon 9500+). Here's the info.;

[COLOR=royalblue]1) Is this a problem that can be fixed with new drivers, or would we have to buy a whole new card to recitify it? If so, are there any cards on the horizon that would offer it?
Drivers aren't likely to fix the problem, with the exception of the ATI 9500-9800. There's hope there for being able to use FSAA properly. You are out of luck on NVidia unless either NVidia or us come up with some clever way of solving this problem.

2) Is this a problem unique to hardware + Source?
It's a problem for any app that packs small textures into larger textures. The small textures will bleed into each other if you have multisample FSAA enabled. The best thing to do right now is either buy an ATI card in the hopes that it will be solved there, or wait until the next generation of cards come out.[/COLOR]

Full thread on the matter here. As regards the ATi "possibility", apparently they support the requiste feature, albeit they (Valve/ATi) aren't sure how to expose it, though seemingly they are close.