Well, both Yahoo & MSN partenerd recently and added the ability for adding @hotmail and @msn users to your Yahoo Pal List -- And @yahoo folk to Messenger Mac's list -- so that's a step in the right direction.
I'd be curious to know if - on the PC side - if a PC webcam MSN user can share video...
With the advent of UVC - Universal Video Class USB 2.0 webcams - finding a Mac compatible web cam will be alot easier in 2008 and beyond. OS X Tiger 10.4.9+ and Leopard 10.5 now have native support for UVC webcams - drivers not needed. But finding UVC webcams is tricky, only a very few Logitech...
Fast forward to the year 2008. The smart choice in Macintosh web cameras now are based on the UVC = USB 2.0 Video Class spec. Support for it is now built into Apple's Mac OS X 10.4.9+ and 10.5 Leopard. It's also supported by Windows Vista. So UVC web cams basically Just Work on modern Macs...