A few performance tips for ya, since that game is probably the most crushing on the gpu ever invented.
IMHO, it's worthwhile to at least try to get the game running in Enhanced Dynamic Lighting. To pull this off, try the following steps...
1) The opening camp is probably the toughest part, graphics-wise, so you'll get your worst performance there.
2) Don't even think about putting textures on max. This setting can easily eat up 700-800mg of VRAM, and you don't have that. Drop them down one notch, and you'll be looking at 1/2 that amount of vram used.
3) After you drop textures, next thing is to lower the settings in the dropdowns. Sun Rays, esp. are very crushing. I would put all three dropdowns to low or off, right off the bat.
4) AA only works in DX10, but in any case, you won't be able to turn it on, so don't.
5) If you're still kinda laggy, you can put shadows and view distance on medium for bump without sacrificing much in the way of visual quality.
6) You have to completely restart the game for new settings to take effect, regardless of whether the game warns you of this fact
If none of the above gets you good enough performance, give up on the enhanced dynamic lights and just go to regular dynamic lighting. If you've made the above changes, you should almost certainly find on FDL, you are golden afa frames goes.
Enjoy ... I thought that game is pretty great. Not as great as the SoC game, of course (you HAVE already played that one, right? If not, I would DEFINITELY play that one first!), but it's a good time, for sure.