In the second, you may be looking for configuring the access on an existing IIS server that handles other applications. This suggests another firewall between the IIS server and the Exchange server. Some guidance, though somewhat dated, can be found from Microsoft in their "Planning and Deploying Outlook Web Access white paper (http://members.microsoft.com/partner/products/officefamily/outlook/deployOutlook.doc). One additional thought, there are some known issues with Exchange servers, and Outlook clients when running through a Pix firewall. These stem from the differences in Microsoft's SMTP implementation from the RFC 2821. The PIX configuration guide for your version should be helpful as well as information found in "Cisco Security Specialist's Guide to PIX Firewalls" by Vitaly Osipov et al.
This was first published in August 2003