I managed to connect to my sons pc over a broadband to broadband connection, I did this using the remote desktop feature on winxp pro from my win2k machine. I did try using vnc originally but i didn't have much success, I dont think I had it set up right. Pcanywhere is usually a reliable remote controll connection.
I imagine, as long as you have destination ip addresses, you can connect to any pc, whatever its connection. If they are behind firewalls, just make sure you have the relevant ports configured.