This depends on the level of protection attempted by the programmer. The short answer is yes, as I am sure this is your code (and therefore it presumably isnt obfuscated or encrypted) you are trying to reverse for testing purposes, as, decompiling someone elses code would be generally wrong.
A quick Google for .NET decompiler, or more specifically one I used a while back to test some code obfuscation, "Reflector for .NET", should turn up some help.