Design client in C#

Hi,

I have to design a client for a web service. But the web service can only takes 10 concurrent request (as it has only 10 concurrent licences). So if I fire 1000 client at time the 950 request are rejected.

Each time client will login with different user name and password. How to efficiently design a client so that no request is rejected. (it is okay if client waits for the connection)