can I load legal copy of XP Home over the top of illegal copy of XP Pro?

From: Laurie Hand*** (anonymous_at_discussions.microsoft.com)
Date: 06/22/04 

Date: Tue, 22 Jun 2004 02:20:35 -0700

I have a 'vanilla' copy of XP Pro loaded on my computer
and want to load a legal copy of XP Home. Can I do this
safely over the top of the illegal copy or do I have to
do a complete replacement? (I want to save my files and
settings etc)
How do I do it if it is possible?

Cheers