I don't know about USB's network capabilities, Firewire should work though - I used it to connect two Windows PCs once and two Macs more than once.
If you use a network cable you could go over the router, if it has enough ports.
If not, than just connect both computers directly.
For setting up the file sharing look into a search machine or MRoogle with "network settings Mac OS X 10. (your version here) and Windows (your version here)".
It may be tricky to get it to work, but sometimes it works like a charm.
Have fun learning.