OWA Setup on a standalone (no exchange) server?

Hello everyone,

Here's my trouble... We were in the process of migrating from Exchange 5.5 to Exchange 2003.  We had all but a few mailboxes migrated over and were running them in tandem for a while.  I finally decided to stop using 5.5 at all, so we migrated a few non-important mailboxes off the machine, did all the other things we needed to do to stop using it, stopped the services on it, and updated our PIX515e to point the email to the 2003 server.  Email is flowing through just fine, but ever since we made the switch... OWA doesn't work externally even though I changed nothing relating to it on the firewall.  It comes up just fine inside the office but not outside.  

So after spending time on the phone with Microsoft and Cisco, they've told me I can't run OWA and Exchange on the same server cause the firewall for some reason won't route traffic for both services.  Something about priority in the static routes on the firewall.  So... Cisco recommended I move OWA to another machine and just reroute OWA on the firewall to that box.  SO... I guess my question at this point is, what do I need to do to setup OWA on machine seperate from Exchange?  Can I just install IIS and OWA without setting up another Exchange Server?  Are Cisco and MS correct about the firewall?

Hope i'm providing enough info, and thanks for any help offered.