Is it possible to install OWA 5.5 and OWA 2000 on the same box? We currently have Exchange 5.5 and Exchange 2000 servers. I've been told that you can use OWA 5.5 with the two but cannot use OWA 2000 with Exchange 5.5. The people on Exchange 2000 would really like to have the OWA 2000 feature. Is it possible to install both on a server and have URLs directing to two different sites?
No, you cannot have both versions running on the same system for the simple reason that you cannot have both version of Exchange on the same system. In Exchange 2000, OWA is part of Exchange; there is no option to NOT install it. Once you install Exchange 2000 on top of Exchange 5.5, OWA 5.5 is completely replaced with OWA 2000. Therefore, you are going to need a second OWA server if you plan on using both versions of OWA.
When using OWA in a PtOz (e.g., Exchange 2000, formerly codenamed Platinum [PT] and Exchange 5.5, formerly codenamed Osmium [OZ]) environment, keep the following in mind: you can only use OWA 2000 to access Exchange 2000 mailboxes. You cannot use OWA 2000 to access Exchange 5.5 mailboxes. OWA 2000 is tightly integrated with Exchange 2000, making this impossible. You can use OWA 5.5 with both Exchange 5.5 and Exchange 2000 mailboxes. This is documented in KB article Q260832, among other places.