Kirk has a post that talks about different ways of dynamically invoking a web service. 

He also mentions a tool called Web Service Studio.  This GotDotNet tool is very nice for testing Web Services but they have removed (or never posted) the source for it.  The last release was back in 2003 and their have been several bugs found, especially when trying to use it with .NET 2.0 stuff.  I hope whoever at Microsoft wrote and released this will come out with a newer version or just release the source code for it and let the community do it…