This is how to get UPNP sharing working from your router using MiniDLNA. I also got sharing working via UShare, but will write this with MiniDLNA because ushare is less compatible and no longer in development. This is a pretty straight forward and simple process if you're familiar with working in the DDWRT environment. The guide is derived from my install using a Buffalo WZR-HP-G300NH running Buffalo's official DDWRT distribution, svn 14889, but can be used for other builds.
Edit: Buffalo's official build mentioned above does not work with inotify. This module in the program allows scanning...