Windows milenium

I have a older Dell computer with Milenium on it.It was a great computer until my daughter put a downloaded game on it.I’m not a computer whiz so I need help to this question.
I was told that I can take the Milenium off that computer and put XP on there,which I have the discs for.Can someone please give me detailed instructions on how to do this?My e-mail is zepplindio@yahoo.com