What's the most appropriate server OS for my needs?

My company needs to deploy a Windows-based server for secure administration of testing.

It needs to be Windows 2000 or 2003.

I’ve looked on-line (albeit briefly), but was confused by the veritable plethora of server options and the widely varying prices. I know next to nothing about Windows server, and know that there are people here who can set me on the golden path.

Price is an issue, as this is really only going to be a small-scale deployment of 10 networked machines initially with 20 machines planned for late next year.

Everything else is pretty standard, I believe – 100mbps ethernet connection, 80MB of network drive space, multicast enabled.

We have a PC that’s plenty capable of such specifications just sitting unused and unloved in the basement.

Thanks muchly in advance!