This is a great document from the Microsoft Patterns and Practices folks, who are consistently producing some great stuff.  I had the pleasure of working with PAG in the past and I’m really digging the whole Patterns series.  

Find out how to ensure that your Web service will work across multiple platforms and programming languages and with other Web services by adhering to the guidelines set forth by the Web Services Interoperability (WS-I) organization in their Basic Profile version 1.0.
[Microsoft Download Center]