The computers are already networked. Set any folders that you want to have available over the network as "shared" by right clicking and selecting the Sharing & Security option. At least one folder in each PC should be "shared".
Any firewall software needs to be configured to allow access to the networked computers, which may involve adding their IP addresses in a "trusted" section.
If you then go into "My Network Places", you should see icons for both computers and expanding the folder tree on the left should show the shared folders in each PC.