Install Quantum GIS on Windows XP, Vista, or 7

1. Download QGIS "Windows Standalone Installer" for your OS (32bit or 64bit) from http://www.qgis.org/
2. Double click on the downloaded .exe file to install
3. Accept the install defaults to complete the process
4. launch QGIS and proceed to the next section on navigating the application menus

It's really that simple.