In version 1.0 of .NET Framework it was possible to test simple web services through web browser. In version 1.1 the feature was disable for remote sessions for obvious security reasons. It still works on localhost, but from remotemachine you only get "The test form is only available for requests from the local machine." message.
You can change that behaviour if you add following code to the <system.web> section.
<webServices>
<protocols>
<add name="HttpPost" />
<add name="HttpGet" />
</protocols>
</webServices>
You can similary turn off remote testing in framework 1.0:
<webServices>
<protocols>
<remove name="HttpPost" />
<remove name="HttpGet" />
</protocols>
</webServices>