I think Am found out why MSN Messenger keeps disconnecting when using a router. He said it's because of uPnP, or Universal Plug 'n' Play. Older routers don't have uPnP and wind up dropping packets that are sent to the computer, resulting in a dropped connection. The solution would be to update the router's firmware or turn the firewall off. This should work if you have a Linksys router. Unfortunately, I don't think this works for the Airport Extreme.