Windows Server 2003 licenses

Hey guys,

I've got a question in regards to Windows 2003 Server licences. We are setting up a backup server in a datacentre, and we are going to allow a few clients to send their backups to it, across Secure VLAN, via S-FTP over SSL.

My question to you guys is, what kind of licences do I need? Can I just stick an OEM on it, and that'd be it? Or would I need multiple CAL's and an SPLA licence?

If it's too expensive, ill just go to a Debian box :)

Cheers,

Andrew