Dear Mike,
There is a little tidbit in https://www.torproject.org/docs/tor-doc-relay.html.en
"e. Leave Attempt to automatically configure port forwarding clicked. Push the Test button to see if it works. "
The "Attempt to automatically configure port forwarding" is in the Basic tab. This setups the port forwarding automagically via uPnP. It worked last time I used Vidalia (the GUI) on a Linksys with dd-wrt router. (I have since manually configured my port forward because I removed Vidalia and am running bleeding edge tor binaries)
The checks mentioned by the others are useful, but if it doesn't pan out at least try the automatic method.
All the best, RgC