You can customize the design of a web service's test page with a single line of code in the web.config file. But like most things in ASP.NET it is not that easy if you actually try it! Although you can find instructions on how to specify a custom wsdlHelpGenerator...
After I wrote my last blog post I did a search for ASP.NET design sites and found an old set of design templates on MSDN. http://msdn2.microsoft.com/en-us/asp.net/aa336602.aspx This appears to be a special section of MSDN that Microsoft created for designers...