I've been playing with my new dlink firewire web cam for about a week now and had lots of fun using iVisit for any cross-platform video conferencing. iVisit is freeware and requires (free) registration with iVisit themselves in order to use the service. Once the straight-forward form is filled in and you've received your email with access password you're almost ready to go.
iVisit's UI is not what you would expect from a proper OS X app, but hey, connection and software are free with the "lite" version. Which part of "bargain" don't you understand?
iVisit is not a patch on Apple's iChat AV, but as long as iChat cannot be used on Windows iVisit remains the yardstick.
click here for Download for OS X version
click here for Windows XP/2000/NT/ME/98 version
click here for the iVisit web site