Would someone care to point me in the right direction?

I have a small LAN, Windows PCs plus a Linux server - ADSL connection, dynamic IP. The server has no GUI or keyboard. I want to run a file-sharing client on the server (24/7) and access it through any of the PCs (sometimes).

This sounds standard to me, but I don't know where to start. Can anyone help, please?

And yes, I know I should RTFM. And I would, if only I knew which M to FR! Ive searched around the sites and the forums, and I still HGFC.