I'm no real expert on graphics but I've got quite some experience in improving FPS, graphics and pcs in general for several games now (FarCry 1 & 2, Call of Duty 2 & 4) and now I'm new to ARMA II.
I'm running a NV-110 gamer pc (quad core, 260GTX, 4Gb Ram DDR2, Vista 64). Haven't checked FPS (still learning all the controls :D ) but as soon as I take a look I'll post again.
For the time being, for ALL fps games a few tips maybe everyone already knows but very useful for those who don't:
1. Match Screen resolution with ingame resolution.
2. Depending on screen (TFT or CRT) try to achieve the highest Mhz value and if possible set the same in game.
3. Configure your graphic card to SINGLE SCREEN, and
4. The most important!!!
ALL recent ATI and NVIDIA graphic cards have a TRIPLE BUFFER option. This TRIPLE BUFFER is USUALLY (not to say ALWAYS) set as default to OFF/DISABLED/DEACTIVATED, etc. Enable this buffer and an increase in FPS will be WELLLLL noticed.
There are other settings to be taken in consideration but like I said I haven't gotten down to check ARMA II yet.
Follow the 4 basic steps I mentioned and enjoy!!!