Finally, after a long research viewing brochures from almost all webcams being sold in my country I found one which WORKS the genius LOOK 315FS !!!
It's much cheaper than the isight AND it has a built-in MIC which is great for mac minis.
Both the webcam and mic are connected through the USB port and I repeat one more time it WORKS !!!
The bad: Webcam quality is average, the design is a replica of a football ball so you have to hide it ... or ignore it.
The good: Works with Mac and Windows, Mic solution for Mac minis (don't expect high quality, good for chat), very cheap (around u$s 35 in Argentina).
I've tested succesfully in Windows XP Professional with bootcamp 1.1 in MSN, Yahoo Messenger, Google Talk and Skype. (Audio and Video)
Mac OS X 10.4.7 with Skype 1.5 (audio) and Yahoo Messenger 3.0 (video), because all other IM programs are only chat capabilities. (I've noticed a 1 second delay in audio and video)
I hope it helps.