custom home server security?

Ok,

I have a dekstop with windows xp pro. I have 4 hard drives in the machine. It is just for a home file server to store files. But i have 4 other computers in the house that can access it. and 3 laptops on wireless. I have a wireless router hooked up. Even tho the router is is password protected im still looking on how to secure the server. I want it password protected so anyone who access the server from the network needs to enter a password. Im just using basic windows file sharing for right now. Anyone know a better software ?

This isnt a web server just a home server.


Thanks Guys