You are on a mac and the mac version of the msn is very poor no audio-video you need a similar tool like msn that runs mac can connect msn users normally with all the functions chat-audio-video

There are a couple msn chat for mac, you could have adium, amsn (it is very similar and supports video chat) you could have messenger on mac That's all I no. Note: I use amsn and adium because with adium you can have more then one msn at a time. eg. google talk and msn.