Section 1.1 of the Windows XP EULA (End User Licensing Agreement) states: ''Installation and use. You may install, use, access, display and run one copy of the Software on a single computer, such as a workstation, terminal or other device (''Workstation Computer''). The Software may not be used by more than two (2) processors at any one time on any single Workstation Computer.'' Although you can use the same CD for each computer, you must either have a volume license or multiple licenses in order to install Windows on multiple computers, whether they are all for personal use under one roof and internet connection or not. If you do try to install it on multiple computers you won't get very far, as Microsoft keeps track of the hardware Windows was originally installed on...if it doesn't match, Windows won't activate. For more information, click here to see if your other computers qualify for an upgrade, which will save $100 each, and here for ordering information. (Note the link on the right, where you can order just another key.)

Hope this helps,