Here are the broad principles -- details may vary depending on Windows version.
Enable file sharing on the appropriate folders. Temporarily disable any firewalls on both or all machines. Make an accurate note of the computers' names (See Control Panel, System -- or equivalent in newer Windows version).
Go to My Network Places, Add a Network Place and follow the Networking Wizard.
May be even easier in Win7 -- bring up Windows Help and type in some key words.