I have a Mac Pro which I've bootcamped with Windows 7 64-bit. I cannot video chat with a colleague that is on a Mac using iChat.
I've tried both AIM Pro 1.5.0 and AIM 7.3.12.3 with no success. I am using a Linksys WRT54G-TM - I tried following the instructions listed below for opening ports for iChat but with no success:

I even tried opening up DMZ to my computer but this didn't work either. When a request is sent to me and I accept, it times out on my end and the other user receives a message saying I declined. When I initiate the request it sits there waiting for buddy confirmation on my end and it times out on their end. When I boot into the Mac side and use iChat there are no issues. I've tried completely disabling the Windows firewall with no success.
My colleague is using AIM through iChat - not a .Mac address. I have successfully video conferenced with another user via iChat v5.0.3 to AIM 7.3.12.3. This seems to me to be either an issue with the Windows firewall or possibly a networking issue at the ISP level.