If you're having Player to Player connection issues like that in RA3, you shouldn't portforward. Your best option is to set your computer as the DMZ. Obviously, if you do that, it may give your friend problems if he wants to play RA3 at the same time as you on the same network. Is that the case?
I know this is an old post, also early merry Christmas and new year to everyone. Also Toxic, I would understand, I do, I mean. DMZ is always the easier way to fix usually the port forwarding problems. Still wouldn't suggest it, only if you're having really big problems with the Router and the Windows' Firewall itself (being not cooperative), otherwise, better the trouble and keeping yourself (a little) more secure and not exposing yourself to "hackers" or anyone who decides to do anything malcious from a DMZ-free connection.