Sigh.
Still having no luck. Have installed DayZ commander, and had it update Arma 2 and the DayZ mod, and install Epoch.
But every server I try to join tells me I can't because I have a bad version.
Install A2, run it from steam, exit, install A2 OA, run it from steam, exit, install patch, run it as admin, exit, install Dayz commander, install mods of choice and play.
If you don't run them before patching it doesn't update the registry.