What do you need?
An SSL certificate for the machine you are running this on, you will need to encrypt the passwords otherwise it will come across as clear text.
Windows Option Pack 4 (I hope you have IIS v4 running)
Setup your webserver andinstall the SSL certificate for these protocols (LDAP, POP3, IMAP4, and WWW)[the one certificate will do], Set the server to use Basic Authentication (same thing for the 'Exchange' site referenced below)
Re-run the Exchange Server setup this timeselect the OWA installation files. Re run Exchange SP4. Test initial connectivity.
In IIS, set the properties for the 'Exchange' site to require encryption (everyone will have to hit the server through its https:// setup)
In Exchange Administrator, Site->Configuration->Protocols, set all the Protocols Authentication to use Basic/SSL authentication, by default it uses all available. By limiting it to just Basic via SSL every communication is secure.
You will have to do testing and write up documentation for the end users, but this system works exceptionally well. I have done this for our outside consultants and it has been running in that configuration for almost 2 years.
Hope this helps. Let me know if I can answer any more questions about this.
