This dialog allows you to change the number of allowed simultaneous internet connections that MS based web applications allow us. For Internet Explorer 4/5/6 and wininet based applications, this is normally only two (IE. A maximum of 2 simultaneous connections are allowed to a particular server).
Example: Go to a web site and open three web pages at once using Internet Explorer 4/5. The third will not open until one of the first two pages has completed downloading. MS have done this because they are following the HTTP 1.1 specification and industry guide-lines.
For the full story see MS web article Q183110:
http://support.microsoft.com/support/kb/articles/q183/1/10.asp