In the future you'll find the latest Arma2 beta build here:
http://www.arma2.com/beta-patch.php
It installs itself as a modfolder called
beta and comes with a new arma2.exe, so it doesn't overwrite anything. You can return to the last "full" patch any time you want. At this time the newest beta-patch should be fully MP-compatible with the normal patch.