You can connect two computers through a home network or directly using an Ethernet crossover cable, as long as both computers have network cards installed. Windows 7 has a Homegroup function that makes sharing very easy if both machines are on the same network. The cable method is completely private and is a better choice for temporary connections or non-networked computers, provided that the computers are close enough to be joined by a physical cable.
Turn on both computers and connect them to the network.
Click on "Start" on one computer, then choose "Control Panel" and "Network and sharing centre." If your current connection is not described as "Home Network," click on "Connect to a network" then on "Change," and select a home network from the list.
Create a homegroup. On one computer, click on "Control Panel" then on "HomeGroup," and choose "Create a homegroup." Check the boxes of the libraries you want to share. On the other computer, click on "Control Panel" and then "HomeGroup," and click "Join now."
Change the libraries you're sharing or add additional libraries by clicking on "Control Panel" and then "HomeGroup" on the computer that contains the libraries you want to share. Under "Share libraries and printers," click the check box for each library you want to share, and then click "Save changes."
Share other files and folders by right-clicking on the folder or file name and selecting "Share with," then "Homegroup (Read)" or "Homegroup (Read/Write)."
Turn both computers off. Connect one end of the crossover cable to the network (RJ-45) port on the laptop and the other end to the network (RJ-45) port of the desktop. Turn both computers on and log in to Windows as usual.
Configure both computers to be in the same workgroup. On one computer, click on "Start," right-click on "My Computer" and left-click on "Properties." Select "Computer name, domain, and workgroup settings" and click "Change settings." Select "Workgroup" and type in a name of your choice. Follow the same procedure on the second computer, and give it the same workgroup name. Restart both computers.
Turn on network discovery and file sharing. On one computer, click on "Start," then "Control Panel." Choose "Network and Internet," and then click on "Network and Sharing Center." Double-click on "Unidentified network" and under "Network," click "Turn on network discovery and file sharing." Select "No, make the network that I am connected to a private network" and click "OK." Icons for both computers should appear in the Network window. Double-click on each icon to share files and resources.
Make sure the workgroup name is exactly the same on each computer.