Google Talk is slowly gaining momentum as a popular means of publicly-accessible IM. After all, it's based on Jabber/XMPP! But as it's experimental, we'll allow it only for a limited set of users, like your boss! Since there aren't many people using the gateway, you can also enable the mail notifications for this gateway. Google Talk also has the added option of displaying buddy icons (small thumbnail images, generally scaled user images). Once you've saved the options and tested the gateway, it's time to head on to limiting the users.
There are two ways in which you can limit the users who can access a gateway. One is by selecting the These users and/or groups can register option button, clicking the Modify Users link and then entering the list of users in the text box that slides open.
The other option is to add these users manually. This might not be a good idea if you want to limit access to a large number of users. But...