Removal of Ex 5.5 from Ex 2003 Env

We recently had a 5.5/2003 mixed environment so we could migrate all users over to the 2003 exchange server. All the users have been migrated and the Ex 2003 server has been setup with the connectors and is the main emailing server. We now need to remove the old Ex 5.5 server from the group of servers. Ordinarily I would have right clicked on the server in the Exchange System Administrator and selected to remove the server. However. The server is no longer running, it was rebuilt before the Ex 5.5 was removed from the server group. So we have our old server still set as a email server in the domain. But cannot remove it!!

I want to remove this old server from the domain but cannot the traditonal way. How can I remove it?

Many Thanks.