Upgrading from 2000 professional to XP

Tech-Archive recommends: Fix windows errors by optimizing your registry

From: hvac45 (hvac45_at_discussions.microsoft.com)
Date: 07/24/04 

Date: Sat, 24 Jul 2004 05:22:01 -0700

I have 4 computers and a server running windows 2000 proffessional, can I simply install XP proffessional? Will I lose my existing files? Can I buy one upgrade program or do I have to get one for each computer? Since all of my business records are in the computers I do not want to lose anything. Any help would be appreciated.