I'm trying to get MSN Messenger working for a friend. This is the first time I've played with MSN Messenger ever but I understand the general requirements.

When starting a video conference (i.e. two-way) from either end it only works in one direction. Always the same direction though regardless of where it was started.

Using the "Send My Webcam" feature works in either direction so I am reasonably confident in the drivers, firewalls etc.

Tools->Web Camera Settings works fine at both ends. Using the video/audio tuning wizard doesn't work at one end - it says the video camera is in use when it definitely isn't (this might be the problem but I can't see why it's happening).

The end that gets through the audio/video tuning wizard no problem is OK I think since it seems to work with another user. Unfortunately the other end is literally half a world away so I can't easily look myself. Even if I could I wouldn't really know where to start.

Firewalls don't seem to be an issue at either end since I can get video at either end in some form, just not both at the same time.

Any ideas?

It's possible that the problem is NAT rather than firewalls. I've seen some situations which choke because the NAT can't figure out where to direct a certain port for more than one data stream. You can get one data stream going through a certain port into the NAT just fine, but try to do a second one and it dies.