I have the SAME exact problem and it has been driving me nuts. The 158 drivers work fine but all Nvidia drivers up to present all create that issue for me. I also have 4GB of ram in 32-bit Vista although it is only detected as 3.5GB since I'm on the 32-bit version.
Bohemia, PLEASE HELP! No other games have problems for me. I want to have the latest drivers for my DX10 games and still be able to play ArmA.