An easy one, but anyway... When building a target in NAnt that depends on a Web Service, the only change to your <vbc> or <csc> task is to make sure your sources include the Reference file that Visual Studio generated when you added/updated the Web Reference, as so:

<sources>
    <include name="MyProject\*.vb"/>
    <include name="MyProject\Web References\RemoteInterfaceWS\Reference.vb"/>
</sources>

I was also pleased to note that in cases where the wsdl imports a typed dataset (ie the remote Web Method takes or returns a typed dataset), Reference.[vb|cs] includes the dataset definition.  No need to add a step to execute xsd.exe!