Perhaps you should consider a homeserver with the amount of machines you have.
It would provide the following things (plus TONS more)
- centralised backup
- 'smart' backup that makes good use of space. Backup 1 Windows 7 PC and it might take 5GB space, backup Windows 7 PC 2 and it might only take an ADDITIONAL 20
MB of space - it only usese the difference
- Backup is automatic and very quick
- works over wireless (although first backup should be done wired to router)
- Centralised file sharing
- keep all your documents, music, videos here
- makes changing computesr easy
- Music
- I keep all my music and can stream it to various players around the house
- remote access
- forgot a file and away from home? Log into the server (free domain) and access your files
There is an awesome server here with 100 quid cash back:
http://www.serversplus.com/hp_proliant_microserver - all you need is the operating system (Windows Home sErver 2011 - 30 quid) and the driver for your storage (comes with 250GB boot drive).
You will never look back and blows the socks off those crappy NAS boxes.
For the advanced folk, you can remote desktop to the server and use it like a normal server for additional services, etc.
BG