You will need a driver to use your USB or FireWire Webcam at all, with any software (iChat or another chat client). These drivers are not really built-in to Mac OS X, with the exception of the iSight. So, if the Webcam you choose does not have Mac drivers, you will need to use the IOXperts driver.
If you've selected a USB Webcam or a FireWire Webcam that does not use DV, then you will also need software to allow you to bypass iChat's requirements. You can do that with the iChatUSB software. The iChatUSB software is not a driver for the Webcam itself, you'll still need a specific driver from the manufacturer or the one from IOXperts.
-Doug