I can think of an immediate solution that is cost effective, and no one would end up having to download AIM , MSN, Yahoo, etc..
But this would be only as far as that.
There's this thing that you can add as a plugin called a "shoutbox" for forums-- Have you ever seen those?
Wadday's Web Development
here's an example I just googled up, but its on a inferior forum programming, fusionboard.
Vbulletin is known to be one of the most secure boards across the net, other popular ones like PHPBB, XMB, yadda have potential iframe problems where scammers "can" keylog what you are typing. Although, there is a problem, I remember reading somewhere on vb's site that they won't nor will ever have plans to implement a shoutbox.
For the shoutbox -- it's a (1st or 3rd party) Box with simple chat functions, everyone who is currently logged on can say something just simply on that section without having to do anything else.
Granted, its easier said than done though. There's going to be a programming headache side to get it implemented smoothly, plus have to deal with potential spamming, crashing.. blah blah! Alex being the admin, might be trouble or a hassle for him to fix it if it goes down too often.
Everything good has always got some deficits.
Otherwise we go back to the standard chat on AIM thing, or create a separate page on another section.. which I can see this can cause further headache potential for Alex