We have Server 2003, happily running OWA over a no-ip.org domain, with the OWA folder being blahblah.no-ip.org/exchange/

No problems there, that is until I have to try and configure our information system's external access ("portal"). This needs mapping to the internal portal link server:82 and for the life of me I can't see how to do this without (a) getting a second domain, (b) losing OWA or (c) setting OWA or the portal on another server.

I've tried using a virtual directory for the portal, it doesn't work properly. It was set up as /portal/ and only half loaded the site. I'm advised by their support to route external traffic to port 82 on the server. Am I right in thinking I can only route to port 82 by sending all traffic there? This would surely stop the /exchange/ link from working, right?

The internal portal website is set up on the same server (as a separate site) in IIS manager so when I try to redirect external traffic to server:82 it conflicts.

Having only ever fiddled with minor parts of IIS before, and having no-one here who has any more experience, I'm hoping someone can help! Sorry if some of this needs explaining, ask questions about my setup and I'll try to answer them.