The best information to be found for Web Services is available in the user guide. If you have not done so yet run the original downloaded Dynamics SL Setup, and install the user guides. By default, they install in the application folder of SL on the server. this is located here on my machine: (\\Program Files (x86)\Microsoft Dynamics\SL\Applications\User Guides). Then in this folder there will be a Web Services Guide.
Let me know how it goes.