I assume your question is somewhat on the order of "How can I
change the resolution without going thru the Dialog box?". That
is, you KNOW what the resolution is that you want, but you're
not quite sure of how to pass the required elements to the
function that does the actual setting.

Given that this is true, there is an API called GetMessage. What
little documentation I have says:

The GetMessage function retrieves a message from the calling
thread’s message queue and places it in the specified structure.
This function can retrieve both messages associated with a
specified window and thread messages posted via the
PostThreadMessage function.
If you can grab and analyze the message posted from the dialog
box to the dll, you'll then be able to replicate in your own code.

This might not be too easy, but hopefully it will get you started on
the path.

http://www.allapi.net/
has an API viewer that might help.

Good Luck and HTHT