I did some research myself on this issue. Microsoft intends to sell the licensed copy of XP for single machine (home users) only. When the laptop is sold with XP, the product is pre-activated. The hardware details of laptop is stored in windows/system32 as wpa.dbl, if XP is loaded on to a different system, it finds all or most the hardware different from the original. This will prompt the user to get license reactivated and get a new key. A key is unique to a machine, so a borrowed key will not work on geniune versions. User has to call microsoft and give them a long series of number and if they are convinced that XP is being loaded on single machine ONLY, they will issue an activation code. This is the only legal way out.