Generally a good idea to search for stuff before asking.http://www.mircscripts.org/
-> Search (BUTTON) -> "Dialog"
The very first .dll that comes up is "DCX," many people use this to modify their dialogs. (Though, I personally don't use it.)
There's not a ton of DLL's on the site, but you can browse through just the .dlls and see which do what by reading their descriptions.