Exchange 2010-2003 co-exist issue

Hi Guys,

I'm trying to start a migration of all mailboxes to an exchange 2010 server from an exchange 2003 server,
I have done pretty much all the setup and migrated one of the mailboxes.

My issue is that i cannot get mail to pass between exchange 2003 and exchange 2010 mailboxes.

Now I am assuming this is a connector issue but cannot see a way to setup the correct connectors via the system manager within exchange 2003.
(Still wanting to use the 2003 server as main server for incomming and outgoing mail but just want to also be able to transfer any all incomming and outgoing mail from the 2010 server - through the 2003 server)

I did the above a while ago when moving to a new exchange 2003 server just by making sure the connectors were in place to route mail between the 2 servers, i.e. using the main server as a local bridgehead and smarthost on the connector from the new server)

I cannot seem to select the new exchange 2010 server as a local bridgehead though via system manager on exchange 2003 - it just doesn't appear as an option.

Any help would be most appreciated, even if i have to go back and do bits of my setup from scratch as long as i can get this working.

Do i need to setup the connectors on the exchange 2010 server? I have partially tried this but still cannot route mail between the servers.
(also just to note, internal mail is also not working between the exchange 2003 and 2010 server)