does multiplayer work across different programs?

This is one of those silly things that i've just never been sure of. So using borderlands as an example; if i own a retail copy and someone else buys it on steam, can we play together or are their onlines separate?

And what about onlive?

Depends on whether or not it's a Steamworks game. But as I recall Borderlands uses an online system that doesn't rely on Steam so I think you should be able to play Borderlands so long as all players are playing on PC. But then again I could be wrong so it would be best to check it up with these guys: http://forums.steampowered.com/forums/forumdisplay.php?f=729