I would recommend setting up static DHCP if your router supports it. That way when your box asks for an ip ... it will always get the same IP.
What I don't know.. is if the wireless dongle has its own mac ... if it does, then you have the problem of needing to make sure the wireless dongle is *not* plugged in when you setup the DHCP for the MAC of the receiver... and that you leave the wireless dongle unplugged while gone.
Doing Static DHCP eliminates much of the network problems when it comes to devices losing connection and getting a changed ip ... ie the "forward your port 5101" ... UPnP works ... but doesn't always work flawlessly.