Maximum Number of Concurrent Connections to IIS6

if the OS is Windows 2000 or XP, then maximum no of concurrent users is limited to 10

if you have Windows 2003 server, it depends on the server memory and application caching..

http://blogs.msdn.com/david.wang/archive/2006/04/12/HOWTO-Maximize-the-Number-of-Concurrent-Connections-to-IIS6.aspx

http://support.microsoft.com/kb/262635