Can IM Virtual Srvr Be An Intranet Srvr?

I’m having a lot of trouble setting-up Instant Messaging for our intranet. I’ve followed Del Smith’s 2/12/2002 TechRepublic article, but I keep getting a message that the user is not authorized to use that e-mail address, and it’s the e-mail addressof the username that’s logged in!

We have the Default Web Site that handles Outlook Web Access (http://email.companydomain.com/exchange) and also an intranet site at a different IP that’s accessible only from our frame relay network (http://companyname). I want to put the IM Virtual Server on the intranet site, but am a bit confused on what needs to go in the IM Virtual Server Wizard’s fields, particularly the DNS Domain Name field.