p2p for my network only?

[assorted]

again; i'm posting a question here i could easily research myself but figure it's a good question for 'the archives'... hehe.

i want to share files between my mac and my pcs. there are programs for macintosh that will allow this; but they all cost money and i haven't found a cracked version of one yet.

so is there a p2p i could run on all the systems that will remain only on the network if i tell it to? and, of course, the smaller and more stable the better...

if not a p2p, can anyone think of any other easy solutions that would let us all easily transfer files to each other (preferably without people outside this network getting access to those files too)?