Hi Andrew;
You should be able to connect to an existing Silverlight application entity service by changing the WPF application app.config file.
For example, if I have an existing WPF application called WpfApplication1, my current app.config will contain the following:
<objectServer remoteBaseURL="http://localhost" serviceName="WpfApplication1/EntityService.svc">
<clientSettings isDistributed="true" />
</objectServer>
I have another Silverlight application called SilverlightApplication1 whose EntityService is located on the following address:
http://localhost/SilverlightApplication1/entityservice.svc
To allow my WpfApplication1 to connect to this SilverlightApplication1 EntityService, I just changed my WpfApplication1 app.config to the following:
<objectServer remoteBaseURL="http://localhost" serviceName="SilverlightApplication1/EntityService.svc">
<clientSettings isDistributed="true" />
</objectServer>
If you have already tried this, could you give me more info as to how your existing Silverlight app is configured and deployed? Any additional info on what you have tried and didn't work will help as well.