Found an interesting paragraph in an iisanswers article. Have not verified this information.
http://www.iisanswers.com/articles/IIS51.htm
Connection Limits
XP Pro allows 10 connections. This limit is installed by default in the metabase key MaxConnections for W3SVC, and there is no user interface method for modifying the setting. You can change this setting to any number less than 40 and it works, but that is not widely advertised.
The ability to increase the connection limit is interesting because you can now increase the max number of simultaneous connections used by IE, on your developer box.
http://www.regxplor.com/tweak11.html