Windows DirectShow Install

I have some code (an exe)? that is dependent on Windows DirectShow. I need the smallest, simplest install of DirectShow that will allow my program to function. Support for both XP and Vista is required. This is really just a research project to find and test the available redistributable code from Microsoft. It will not likely require that any software be written, but knowledge about DirectShow and DirectX and the existence the Microsoft MP3 decoder that is buried in certain versions will be helpful since this is the component I am using. I will provide a Windows program that you can use to see if the Direct Show component I need (the MP3 decoder) is on the target computer. You will need access to a computer that initially fails the test because DirectShow is not installed yet, and then determine a procedure (an Install) for both XP and Windows that will allow the test program to operate.