How do I Get a WCF Service & a Website calling it to execute under your network login rather than NETWORK Service

Question

When I developed a site with VS 2008 it happily connected to a the webservice in the solution, then connected to the database (using ADO.Net Entities) and ran my query.

Now I come to rolling out the site. When it connects to the webservice it is connecting as NETWORK SERVICE - which I don't want - I need it to connect as 'MYCREDENTIAS'.

This way when we want to change a users access - it can be done by the network guys - just by adding or removing users from various roles in SQL.

So the question is -

How can I set up an ASP.Net Website and the Service to use MYCREDENTIALS and not NETWORK SERVICE or for that matter changing my connection to use a fixed login - since then we lose the simplicity of the security role setup on SQL.

My system.serviceModel tag from the WCF Service is as follows;

<system.serviceModel>
    <bindings>
        <basicHttpBinding>
            <binding name="BasicHttpEndpointBinding">
                <security mode="TransportCredentialOnly">
                    <transport clientCredentialType="Windows" />
                </security>
            </binding>
        </basicHttpBinding>
    </bindings>
    <behaviors>
        <serviceBehaviors>
            <behavior name="STG.Services.WCF.Formulary.NationalFormularyBehavior">
                <serviceMetadata httpGetEnabled="true" />
                <serviceDebug includeExceptionDetailInFaults="true" />
            </behavior>
        </serviceBehaviors>
    </behaviors>
    <services>
        <service behaviorConfiguration="STG.Services.WCF.Formulary.NationalFormularyBehavior"
            name="STG.Services.WCF.Formulary.NationalFormulary">
            <endpoint address="" binding="basicHttpBinding" bindingConfiguration="BasicHttpEndpointBinding"
                name="BasicHttpEndpoint" contract="STG.Services.WCF.Formulary.INationalFormulary">
                <identity>
                    <dns value="localhost" />
                </identity>
            </endpoint>
        </service>
    </services>
</system.serviceModel>

The WCF Entry in the client website is as follows;

I have also set up both the service and the website to use Integrated Windows authentication and cleared Enable anonymous access.

The connection string to connect the ADO.Net Entities