Multiple concurrent WCF calls from single client to Service

I have a service that calls a service on another machine and the most number of concurrent connections I can get is 2. I have tried changing the throttling on the WCF Service Behaviour but to no effect. I have read that it is because of the HTTP limit of 2 concurrent connections from a client machine to a server. How do I overcome this? The os on both machines is server 2003.

Config:

<serviceBehaviors>
    <behavior name="MyServiceTypeBehaviors">
      <serviceMetadata httpGetEnabled="true" />
      <serviceThrottling maxConcurrentCalls="100" maxConcurrentInstances="100" maxConcurrentSessions="100"/>
    </behavior>
  </serviceBehaviors>

<system.net>
<connectionManagement>
  <add address="*" maxconnection="100" />
</connectionManagement>