Gosh, had to be an AS3 hater, but I definitely wouldn’t recommend that for a chatroom. Means you would have to use the Flash plugin. Not very post-2010 friendly.
I use BBPress for this. There is so many good plugins these days, I wouldn’t recommend putting your resources into re-coding “the wheel” so to speak. Go with an out of the box solution. Even if you wanted to use the Flash plugin, I’m sure there’s a cheap solution. Even if its $49, $99, you’re talking about a relatively small cost compared to months of writing it yourself.