I saw it's been a bit since anyone posted here, but here's an FYI I just recently solved for my iSight: Most often when a camera is needed for live input, lighting is intermittent at best. A great software fix, in the form of a FW camera driver, comes from IOXperts.com
http://www.ioxperts.com/ "Camera Controller" only runs about $20 US, and for the money it's definitely worth it. I am able to capture clear imaging of a black hand-rail mounted to a stage 30' away, in a dimly lit club, with no direct lighting, through my iSight. It does come at a wee-bit of a price performance-wise, running another program (an imaging app, no less) will eat at the over-all thru-put. [I run a pwbkG4 1.5Ghz w/2Gb ram] However, I found a good balance that gives me what I need by reducing the input values in the Video Capture prefs- buffer/frame-rate/decompress accu. (Right now I'm just putting the girlies shak'n down in the crowd up on the big screen to shake for everyone.) There are a lot of web-chat related options with the driver I don't recommend for VJ-ing, But you have the option of controlling them realtime-ish, so see what your machine can handle. The driver can be test-driven for 30 min. at a time, and comes complete with the usual 'nag-ware' and if you don't use it, make sure to dislodge it completely from your library (Lib- App. Support, -IOXperts) or it will try to tell you that you can only use your camera for 30 min. even if you trash the IOX App icon. I hope this helps out anyone trying to get an iSight video feed running. This works great on PWR-PC, but for Intel, I don't know. p.s. For iSight-plugged-in-and-iChat-turns-on issues, at the bottom of the video options in the iChat prefs, turn OFF the launch iChat when a camera is turned on...
A nerd at play, makes money that day.