Web services aren't "triggered", they're called. Think of them as really really remote method calls.
So, in your case, it sounds like after the code adds the XML to your dataset, it would make a call to the webservice. The power of Visual Studio makes this easy, as all you'd do (from the calling side) is add a web reference to the web service, by right-clicking on the references branch of your project tree, and selecting "Add web reference".
Chip H.
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