As long as they're on the same LAN - both connected through the same router you shouldn't need any software.
Find the ip of one, )generally something like 192.168.0.x) and windows key + r on the other one and type \\<whatever the first up is>\c$ and you should be able to browse the c:\ of the first pc. Then just drag and drop
read that back and it does make about as much sense as a mong smoking crack
browsing the C$ is the easiest / quickest way. http://en.wikipedia.org/wiki/Administrative_share
right click folder you want to share -> properties -> sharing ->share folder
on the same computer, right click my computer -> properties -> jot down the computer name
on the other computer go to start -> run and type \\<computername>\<sharename> eg. \\mypc\music
however all complete nonsense if one of the computers is a mac.