I spend a lot of time using webcams. I would strongly advise you to get the Logitech 3000 or 4000 series, or a 3com homeconnect (3com doesn't make them anymore but someone else bought the rights - not sure who). The logitechs have better drivers.
What you're spending the extra money on is a CCD instead of the cheapie cams which use a CMOS (two different types of chips for "seeing"). The CCD chips are much more sensitive and can tolerate lower light levels.
With any of the above cams listed, I can have all the lights off in the room, and appear in medium brightness to my webcam viewers just by the light of the monitor. This reduces framerate, but that's no big deal.