Ever heard of the "Samba" protocol for file sharing? That's what M$Windows uses if you enable "File and Printer Sharing".
Open up Windows Explorer, and type any IP in the following format:
This will give you the Samba shares on a given computer.Code:\\192.168.0.15\
The whole "Map a network drive" thing simply lets you take foreign Samba shares and assign them to a drive letter on your own computer, so basically instead of typing "\\192.168.0.15\porn\asian", you just type "k:\porn\asian".
By the way, I think Mozilla Firefox can access Samba by doing "smb://192.168.0.15/" (just plucking this from memory, not sure if it's entirely correct)