using logicam with mac

hi folks,
just got a logicam to use with my mac. it works fine, great quality, etc. what i'm wondering is there a way to set preferences so that i can shut off the internal video and use the logicam. certain beta chat systems seem to automatically use the u=internal cam and i can't find an option to use the peripheral... is it possible to choose? it does work for ichat.
thanks!