That's the purpose of MaxiVista. It uses the local computer network, wireless or Ethernet (or Ethernet cross-over cable or FireWire) connection, to extend the Windows desktop to another PC. There are some considerations involved, which we'll look at, but it works with Windows 2000 and up, including XP, Vista, and Windows 7 (in both 32-bit and 64-bit versions).
A free trial of MaxiVista is available from their website. The demo version works for 14 days or 50 startups, whichever occurs first. Hardware acceleration, OpenGL, and DirectX are not supported in Windows Vista or Windows 7- on either the primary PC or the secondary PC. This also means that Vista "Aero" effects are disabled when MaxiVista runs. This may elicit a groan from those who like their Vista "eye-candy," but the previous version of MaxiVista didn't work with the Vista display programming model (WDDM) at all, so at least this is some improvement.
Since I tested MaxiVista on a 32-bit Vista desktop and a 64-bit Windows 7 laptop, I had to download both the 32- and 64-bit versions, which came in zip files of about 5 MB each. Unzipped, three files were exposed. These were "antivirus_check.txt," which seem to only work with Avira antivirus, "Maxivista_Setup_PrimaryPC," and "Maxivista_Setup_SecondaryPC.exe." I dragged the secondary setup file into a shared folder and dragged it onto the desktop on the laptop using the network.
This network, by the way, is a simplified wireless network in which no one computer is the "boss" and the general rule is share and share alike. It works across Windows XP, Windows Vista, and Windows 7, and MaxiVista surprised me by how well it worked with it. You can read more about it in an article here on Bright Hub.
Installation of MaxiVista took less than a minute on the primary PC. Below are the first and last dialogs in the installation.