ISA & Exchange Rules

I've set up a new Exchange 2003 server, migrated or moverd all my mail boxes to the new server. Everything is working well. However, my old Exchange 2000 server is still "on-line ". If I shut it down, I lose all mail flow.
My problem is I have ISA 2004 server rules & protocols that still point to the old server. When I try to "edit" the rules and enter my new servers IP & routing info. I am denied. I'm told the OUTLOOK, OWA can not share the ports. Currently I have a Exchange SMTP rule & OWA rule. Both point to the same IP & server. But I can not edit these to point to my new server.
Do I have to DELETE these rules & then re-create them with the new IP & Server info? Or is there a simpler way?

 

My suggestion would be to disconnect the server from the internet, immediately remove the ISA add-in, and install a third-party firewall program. That alone should solve the problem Or, you could use a hardware firewall for the port fowarding instead...