There are other firewire cams available. The Apple store even used to sell some alongside their iSights. Im not sure if they still do however. Might still be worth looking for elsewhere though..
Not many USB cams are supported in OS X and even once you do get one working, it still wont be any good in iChat until you pay for 'iChatUSBcam' as Oreo mentioned. Could be ok for Skype however.
Also (more of a side note really) The universal MACAM driver is being worked on again. Its a free driver and it allows a multitude of cams to work in OS X, that were not originally supported for OS X by the cams manufacturer. Even the PlayStation eye-toy cam will work with this driver. When I last tried it, frame rates were not great. But its certainly better than the cam not working at all. Plus it means you can use some of the dirt cheap cams commonly available for PC's. And as I say, its free! Unlike the ioxperts driver.
USB webcam driver for Mac OS X