You'll need a couple of things: Link with the user32.dll import library, which is located in DMD\dmd2\windows\lib\user32.lib. Either pass it to DMD during compilation or more simply just can add a pragma(lib) in your source file like so: pragma(lib, "user32.lib");
And you need the function prototype. for windows api it needs the extern(Windows) calling convention. So your code would look like: http://codepad.org/hvOPpP9c You are better off using the WindowsAPI bindings project, which includes almost all windows api function prototypes. You can download and read about it here: http://dsource.org/projects/bindings/wiki/WindowsApi
