Stupid question...  

I cant say that it is right to share the same copy. but if you choose to do so that is your right.. it may not work because if you are using your pc online and registeres your version of windows.. when they install it it will not be able to be used.. also a computer from 6 years ago with windows 98 may not be able to support the xp version.. space wise. unless they are udating the whole system .
hope this helps you out

Well, this isn't a bad question, per se, but I think you already know the answer, somehow. The answer is that Windows XP and just about every other non-open source operating system, is licensed for you to install on a single computer only.

Even Apple has this restriction and theoretically if you want to upgrade both your desktop and laptop from, say, Panther to Tiger, you'd need to buy two copies of the OS.

Realistically, though, I know of few people who follow the letter of the law with operating systems. If someone has both a laptop and a desktop PC, for example, they'll almost always use the same OS install disk to upgrade them both to a new version of Windows.

For Windows XP Pro, for example, you really need to order additional licenses from Microsoft directly. Theoretically, the additional licenses are at a discount, but there are lots of hoops you have to jump through before you can ascertain the exact price. Want a full version of Windows XP Pro? That'll set you back about $300, just for one computer.