is there a way to set the settings on an external webcam? I would like to change the brightness settings of a USB webcam. Is there a way to do that without installing extra software on Lion?
Without - no, not unless your cam manufacturer makes something Mac-specific [but then again, that wouldn't truly be without, just free].

With - I'd recommend Webcam Settings 8 bucks from the App Store.
It's what turned my Logitech from a barely functional lump balanced on my monitor into something actually useful.