The best option I have found (I'm in UK, my family live in Canada) is me on iChat with an iSight and my family (who use PCs) on AOL AIM and their Logitec webcams. If the PCer can use a firewire webcam that will help but otherwise they will get a great image of you and you will get a so-so image of them.
I have tried mac.com and AIM accounts for my iChat account and have had better luck with the AIM account on my Mac. The Mac.com account works fine when it works but I was unable to connect with some folks with it. The AIM works with everyone I've tried.