I'm currently running nVidia's ancient 314.22 because of this problem. The exact versions reported to work longest without a crash differs depending on who you ask, so you're on your own to find one that works for your exact system. The fix is, unfortunately, to downgrade your video card drivers pretty much at random. The decals seem to more frequently trigger the part of the driver that causes the crash, so disabling decals can help reduce crash frequency, but not entirely eliminate the crashes. The problem is that specific graphics card driver builds and Just Cause 2 don't get along.
It's not the decals (it can still crash with them off) they're just related to the problem and can make it worse, but are not the root cause or the way to fix it. I had the same problem (hard, repeated crashes to desktop) and now I can play Just Cause 2 for hours on end before running into the crash. This is a common problem with Just Cause 2.
