No, data discs have different latency requirements from actual DVDs. A stream from DVD or WMV-HD DVD is a sequential stream, but on DivX and Xvid are not sequential files so the head needs to seek = higher spin speeds.
You’re also right about network sharing, it doesn’t work on that unit. To my knowledge the only ones that allow it are the Niveus systems.
As far as making a normal PC a media center extender I’m still working on it myself. I don’t mind so much that it’s a full-blown stand-alone media center, but I’m trying to get my recorded TV to stream to the second media center without mucking about and allow anonymous access to my shares (which I consider a security risk, I like my kerberos). Also, since all of my digital media (ripped music, compressed TV shows and so on) is stored on my 1.5 TB RAID 5 array in the server, that’s easy to share as well.