Removing the last Exchange 2003 server from an Exchange 2010 organization

We're in the process of decommissioning our last Exchange 2003 server, I have proceeded through the steps in the Microsoft guide on how to do this and have deleted both the Mailbox and Public Folder stores, removed the RUS policies for Domain and Enterprise.

All mailboxes and public folders are now homed on the new Exchange so nothing resides on the old Exchange 2003 server.

I have today inserted the Exchange 2003 media into the Exch 2003 server and chosen the remove action, but it keeps telling me;

'The component "Microsoft Exchange Messaging and Collaboration Services" cannot be assigned the action "Remove" because: - One or more users currently use a mailbox store on this server.

I checked the server by searching ADUC and also checked this KB article http://support.microsoft.com/kb/279202 and nothing shows up.

I also checked this article on someones blog but no such luck http://smtp25.blogspot.co.uk/2007/04/having-trouble-to-uninstall-exchange.html

However someone made a comment that the used an ADSIedit query (&(objectCategory=user)(msExchHomeServerName=*)) however I am unsure how to do this in ADSI.

Any advice would be gratefully received.

Thanks!