I put together some packages that let you use your openwrt AP as a media server for the roku and to serve up movies to any browser.
First off, get a router with at least 16MB flash and a usb port for the storage device. The image is big; even with all the squeezing I've done it's 8MB squashed and 11 MB as jffs2. Then get a recent trunk and make sure you can build a good image for your router.
Now get the mediainfo tarball here: http://www.seiner.com/cz/mediainfo.tar.gz and untar it in the package directory of the build tree. Get the roconnect tarball here: http://www.seiner.com/cz/roconnect.tar.gz and untar it in the package directory.
make menuconfig, and enable apache and php5. You need simplexml support in php5, so enable php5, PHP5 LIBXML support, php5-fastcgi, php5-mod-dom, php5-mod-json, php5-mod-simplexml, php5-mod-sockets, and php5-mod-xml.
Enable roconnect; that should require all of the above plus libmediainfo, mediainfo, and libzen.
Build the image.
Configure apache to work with php.
Attach your external storage that will hold your movies. All of the roconnect stuff is in /usr/share/htdocs/roku, the default document root for apache.
Visit the roconnect website http://www.ro-connect.com and set up roconnect for your Roku. You need to pay the $0.99 for the roku channel.
Enjoy.