Question : How to configure exchange 2007/2003 to redirect external users to external url

Hello experts,
I completed my first exchange 2007 install yesterday, and after applying all the patches, hot fixes and service packs needed to install, everything seem to work well, that was until i discovered that mail was not flowing between my existing exchange 2003 and the new exchange 2007 server, i was able to find the solution for that problem on tech net (http://technet.microsoft.com/en-us/library/bb691187.aspx).
after running the script mail was flowing fine and public folders were synchronized, i started by creating a new user in the new exchange server and everything worked, and same thing when i migrated a mailbox to the new server.
when a user inside the network tries to go to webmail the go to the same link that they have always used  (which takes them to the old exchange server IIS) and they are prompt for the uid/pass, if they enter a uid from a mailbox that is part of the exchange 200, they are redirected to the internal URL of the new exchange server and are prompt with uid/pass again (first problem), and once they enter that they are presented with OWA, ok thats great and is not a problem when working from inside the network, but most of my OWA users will not be inside the network (second problem) so if one of my remote workers go to webmail.domainname.com they are taken to the exchange 2003 server and they are prompt for UID/pass, once they enter it and the server determines that the mailbox is part of the other server it tries to redirect the user to the new server, but it does it using the internal URL server2.localdomain.local, which obviously is not registered domain name and is not reachable from the public network, to try to resolve the problem i created a new A record on the DNS settings pointing to another public address(webmail2.domainname.com) and that works if the user goes directy to that URL, but since we are trying to make this migration seamless to the users, and we are going to have mailboxes on both servers, what configuartion or change do i need to make to ensure that the external users are redirect to the public URL instead of the privete URL, and how can i prevent OWA/IIS for prompting the user to enter the UID/PASS twice.

i am sorry for the length of the question, but i figure i describe the environment so it makes more sense.

Thanks
Juan

Answer : How to configure exchange 2007/2003 to redirect external users to external url

You will need a separate CAS server then. It will have to be Exchange 2007 to allow both types of users to access OWA.

Simon.