However, win7 has fairly nice and super easy to use networking capabilities as long as the other computers run win7 too.
I like what you're doing. But why not consider using an ssd boot disc in the htpc and having the server elsewhere. This saves space and noise in your htpc and, for a couple hundred bucks, you have a better htpc and a remote freenas server that works much better at being a server.
I am going to do the same thing..NAS and Media Streaming.. I will go with xenserver, then install Windows server 2008 for file sharing, Windows Home server for streaming, and Windows 7 for media center capabilities, all as virtual machines all running at the same time on the same machine. You have Windows Server as the file server and the media in a folder that is mapped on the other OS's, since the OS's are all in the same machine the performance is fast.
Look for the xenserver..it is the new revolution in virtual machines