XP Upgrade

I’m an IT Helpdesk Manager at a large company who has to upgrade our desktops to Windows XP Prof and Office 2003. We are currently using Windows 2000 Prof and Office 2000 Prof. I want to do a clean build because because there is too much rubbish on the existing desktops, but our Network Manager wants to do an XP upgrade. I need to put together a report to justify a clean build. Have you any case studies or info to help me in my cause?