Hey I have the same exact problems that you are having. When ever I play Arma 2 (mainly editor), my PC freezes, and the only fix is to reboot. But my PC is brand new, and I'm suprised that it's having these issues. Sadly, I don't have any suggestions or anything... I guess I just need to deal with it...
My Specs:
Windows 7 64bit
8-Core AMD Fx-8150
8 Gigs of ram
Radeon 7770 1gb Crossfire X Mode
1Tb Hard Drive