windows on a mac

I found my dads Windows XP disc near his computer and I was wondering if installing it on my mac would somehow screw up his computer?
Also, is it possible to install it on an external hard drive and when I want to use Windows I just plug in the hard drive and load windows?(cuz i dont really have 20gbs of space on mac mac to just waste on windows)

Unless it's a volume license, it's probably not legal.

whats a volume license?

To answer your second question, yes.

Tutorial:

How Install Windows on an External Hard Drive | eHow.com

I believe, though, that you will need a non-Mac system to do that. Not sure.

@Yabz

You asked this same question again in another forum. You were told that what you're trying to do is illegal and the thread was closed by a moderator. I'm closing this thread for the same reason. Also do not cross post.