I would think, if both of you are using the currentest (is that a word? No, but it works
) MSN Messenger, its built-in voice chat function oughta work for you, as long as both machines are equipped and configured for it. I dunno ... don't use it myself. Mrs Timber does, and if she can get it to work, anybody can
I think she prefers Yahoo! Messenger for voice/video chat, though ... not sure why ... I'll ask her. She never uses anything here but Windows machines, but I'm pretty sure some of her freinds are on Macs. I'll try to find out for ya.