Something else PVRWire reported today.
pyTivo lets you stream most videos from your PC to your unhacked tivo. It uses the HMO server protocol. It will guess if your video is 4:3 or 16:9 and pad your video if it thinks it is needed (looked good on my tests). It will not transcode an mpeg that is supported by your tivo.
This is more for the technically adept. You need to install Python, and it is still in a very early state.