First off, thanks for building this guide

A few questions (Caveat: still a newbie so let me know if the following questions make some assumptions I shouldn't be making):
1) I have a couple of nettops just lying around that I was thinking of using as HTPCs. My plan was to load up XMBC on them and have the media server stream to them. Is there any specific process for getting Linux to play well with XMBC or do you know of any other guides out there for this?
2) I know I can use this for streaming media to my TVs in my own house. Is it possible to access this media from a friend's house (i.e. could his HTPC etc. access content on my media server?)
3) Is this server setup only good for movies/music or could I also use it to host various files (e.g backups of my laptop etc.)? Is there another program you would suggest I use for this purpose?
Thanks again!