Re: Upgrade Exchange Server to 2007
You can’t simply “upgrade” where one version replaces the other and everything moves with it. You need to do a clean install of 2007 add it to your 2003 org and migrate your mailboxes from the 2003->2007 server. Once this is done you can remove the 2003 instance and extend the org to fully support 2007.
Or are you asking a totally different question?
See this link.