If all your clients are Windows (XP or newer) I would recommend you with Microsoft Home Server... yeah I know it says "home". Ignore that bit.
This is a dedicated backup and file-sharing server based on Windows 2003. Its not free, but if you've got hardware to throw at it already, you can pick up the OS for around $100 (http://www.amazon.com/dp/B000VWW8QQ/?tag=hashemian-20). Or you can buy a pre-built "appliance" and add drives as desired (http://www.amazon.com/EX490-Mediasmart-Home-Server-Black/dp/B002N8A0A2/ref=sr_1_2?ie=UTF8&s=electronics&qid=1271861254&sr=8-2).
I just finished setting up a custom build at home and I am really impressed. It really makes backups easy... and disk friendly too. It does some kind of changed-cluster recognition on the client and only stores changed clusters. And it recognizes if clusters are the same across multiple PCs (like files in the Windows or Program Files folder for example) and only stores them once on the server... really saving space on the server. For example, I've got 3 Windows 7 machines. Two are basic installs (~40GB) and the last is ~300GB for my laptop. After 3 complete backup cycles its only taking about about 180GB of server storage total.
Recovery is a snap, I tell the server what backup to mount for recovery... it thinks about it for a bit (it's having to build a "virtual" filesystem from the cluster database) and then you have access to the complete backup image for recovery.
It doesn't sound like you need or want the file sharing stuff, but if you do its cool too... if you place data in a share, WHS makes sure that the data is always duplicated on at least 2 spindles (2 drives... kind of a software RAID 0). That way if you lose a drive you don't lose the data.