I am at a stage where I want to build a file server to serve my Ubuntu laptop and my girlfriend's Windows 7 laptop.

Is it easier to stick Ubuntu Server onto the file server or are there better distros for acting as file servers whilst easily maintaining compatibility with both Ubuntu and Windows?

The other thing for me to consider before going ahead to build the server is that I want to build a media center, but I don't know which is the most sensible option. My plan is currently to build a pretty (nice case), but light weight (not too powerful) media box that goes to TV and Stereo and uses the file server via Ethernet or WiFi. I may even consider SSD for the media OS drive if it is using the file server for main storage.

I will probably use MythBuntu for the media center, so I don't know if that points strongly in favor of Ubuntu Server for the file server. Apart from compatibility with my existing systems, I suppose good back-up software and general low-maintenance are other factors.