Thanks to a post by Omri Gazit I am able to minimize the number of 403.9's (Access Forbidden: Too many users are connected to Internet Information Services) I was seeing on my web server today. It turns out Windows XP Professional only allows 10 simultaneous connections by default (What were they thinking $$$). To top it off it turns out that many browsers will open more than one connection.
I bumped up the number of connections by running: adsutil set w3svc/MaxConnections 40
I also set my connection timeout to 120 seconds and turned off HTTP Keep alives. Not the best for performance, but better than an Access Forbidden error.
Hopefully this helps. I don't want to change servers.