I've yet to figure out how to fix the lag problems in Fallout 3. I managed to get AA working. I haven't experienced a crash in a very long time. No idea what I did to fix it or if maybe one of the Windows Updates fixed it or even possibly one of the ATI driver updates.
With AA I found out that you need to set everything in CCC to default and to application controlled, even Anisotropic. THEN you can use 8xAA or whatever you choose in Fallout 3 without any issue.
As for the lag, I was wondering if anyone had found a fix for it. I just started playing Point Lookout and it's really awful when you first get off the boat. Unless you stare at the sky or ground, it seems to only be going at 5fps until you get out of that area. It happens when you look at the horizon, even in buildings sometimes it will happen. It almost seems like the game is glitched to render more of the surrounding area than it should.
I posted a few weeks ago but after I posted my Dxdiag, I hadn't gotten any reply. Was hoping someone figured it out. Also thought I'd post on my AA situation in case any others weren't able to get AA working with Fallout 3.