Forward ports within LAN network

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http://serverfault.com – I have a torrent(transmission) server running on an old laptop. When I want to access it, I can just type torrent.oliver.lan:9091 in the browser and I get the web interface. I want to forward any local traffic accessing port 9091 to port 80 so that I can just type torrent.oliver.lan into the browser. Forwarding outside traffic is easy (as I've done with the torrent port). There is a Source Net column in the DD-WRT web interface which presumably helps me limit the port forwarding to specific IP addresses. I tried inputting and (my desktop PC's IP), but that did nothi (HowTos)