Techy question - a bit off topic I grant you!

I have a question (the best way to set up a web cam video conference between my XP/logitech webcam & and my sister's apple Mac with an Isight webcam) that I have a feeling someone around here might just know the answer. Please, if you know the answer, drop me a private email).

Thanks, experts.

MSN Messenger which is supported on both MAC and Windows XP.

Paul