Check out
www.vbrick.com. Their box(s) are geared toward what it sounds like you want to do. I've used a number of there products which cover the a wide spectrum of content delivery systems. I would recommend giving them a call.
Here is a link to the datasheet for their set top box.
http://www.vbrick.com/docs/VBrick_Datas ... 4HDSTB.pdfAll that said, if you build and install a channel on a Roku that plays off of your internal servers, I don't think it needs general Internet access. I could be wrong, but I don't see why it would need it. Mine does that for the channel I am testing (uses an internal server instead of our WWW host on the cloud) but it does have Internet access too so I can't vouch for the fact that the box will boot and run without internet access.