feed the wsdl to founstone's WSDigger, then go to the top menu and chose to run tests, this will check for commonly known injection attacks.

Sec542 has a whole section on webservice hacking =)

Yeah i noticed that SANS542 does have coverage on it but unforunately i cannot afford the course and dont think my company will pay for it as i have only been working as an entry level pen tester for 4 weeks!

Thanks Jhaddix, much appreciated

Your Silverlight application likely still accepts and processes user input.   That's where most of the vulnerabilities come from.   Using intercepting proxies, like WebScarab, Tamper Data, Burp, and others should still do the trick.   You just to look at the app one request at a time and see what you can do with it.

I have just purchased a book called "Hacking web services" by Shreeraj Shah.  It is pretty old as it was published in 2006 but figured that it should give me a good foundation on on how to hack (provided the book is what it says on the front)... ill leave an update on it once I have read it and provide any tips for those whom may want to know.... If anyone else has any suggestions on books please let us know