For an OS, you might want to consider Windows Home Server. It's quite cheap, even if you don't get help from Jim.
It provides backups of clients, and also has some basic management of backup to USB drive or whathaveyou. Also provides a DLNA media server, and a web interface for uploading/viewing your files/videos/photos, etc.
I've been running a V1 (based on server 2003) box for a couple of years now, and am now migrating to 2011 (based on server 2008 R2). It's pretty good at 'just working'
What Matt said.
If I didn't already have more than the amount of drives to put in one of those I'd buy one myself.
I would quite happily pay a monthly fee to someone if that would mean being able to legally stream/download movies in high quality and I was provided with a good choice of material - I do so already for Spotify (despite its niggles).
But there isn't yet such a service for video material unfortunately. Retarded industry...