If I understand the question properly, you would like to be able to use Outlook 2000 over the internet to access the Exchange Server.
If you dont have a firewall protecting your server (of which I dont suggest, and recommend you get one ASAP), you can simply have then add the IP address and server name to their hosts file, and they should be able to connect. (FYI they will also need the Client for Microsoft Networks installed. The client doesn't need to be configured to log into anything, they just need the client installed.
If you do have a firewall (and should) then you will need to do a little registry tweakin'.
Exchange dynamically assign ports to the Directory service and information store, so you cant pick port holes for your firewall. You will need to assign these services specific ports. MS has a KB article on how to do this:
http://support.microsoft.com/support/kb/articles/Q155/8/31.ASP (please remove any spaces in the link)
Once you lock the ports, client need to dothe same things as above. Have the client and a hosts file with IP address and server name- example:
192.168.10.5 ServerName
