I managed to solve similar problems with my system and ARMA 2.
First off, the individual missions/scenarios have so far been running without big issues. Even when I started the campaign, everything went smooth, apart from occasional slow-downs and stuttering in the coastal cities.
However, towards the end of the campaign I began having constant CTDs (preceded by artifacting), black-screens, freezes and general choppiness. Plus whenever I wanted to save my game, the game just crashed with "cannot commit" -message. I knew it wasn't heat etc. as my graphics card maxed at 75C.
What I did was:
1) I updated the graphics driver to the latest version 190.38, it has an Arma2 -profile (use it and be sure to select the single display mode in the options)
2) "underclocked" my factory overclocked graphics card to the default clocks
(temporary arrangement).
3) set my max/min pagefile size to 9 GB (should be 1.5x your RAM)
4) deleted the "Arma2.cfg" -file from MyDocuments/ArmA2/ -folder. When you start the game it will create you a new one.
5) "cut/paste" all my saved games to the desktop and then back to the same MyDocuments/.../campaing folder. (I'm not sure if the save-files were somehow "corrupt", but this simple trick fixed the "cannot commit"-problem for me).
6) defragged my hard-drive
7) started the game with "-winxp" command line
8) in the in-game video options I set everything to "default" or "normal", except video memory, which I set "very high" as I have a 1GB-card. (You can work your way up from these settings if you start seeing the game being more stable.)
As a result, the CTDs and freezes disappeared, I am now able to save my game + it looks better and runs smoother. I can now run even the campaing 1680x1050 with everything set to high/very high, except texture quality =normal, without major issues.
I'm not saying the game's graphics engine doesn't need optimizing (the game is still a bit choppy when I get near the coast). But by doing these little tweaks I was able to complete the campaing while experiencing OK
performance.
If nothing else, those who have major problems with ArmA2 might as well want to give these tweaks a try. The game's content is well worth it!
My specs:
i7 920@3250
gtx 285 OC heatpipe
6GB ram
Win 7rc