<< A friend of mine bought XP and installed it on one computer. He activated it with no problems. When he tried installing it on a second computer and tried to activate it he got an error message saying it has been activated on another computer and he coould not activate it on another computer.
The only way that could work on multiple computers is if that person is using some sort of activation crack program. If they are not activated one day it will not boot up. A fun time for no one. Better to install Win ME.
You could install winxp on mutliple machines by calling them every few days and saying you installed new hardware so that they give you a activation code. I think eventually, on like the 4-5 machine they would start to get suspicious though. But if it's only 2-3 machines, you could do it easily.