Very Computer

My problem might be a very simple one, but as that I am still new to the
wiles of Delphi programming, I'm having difficulty figuring it out:
I've written a front-end database program that hopefully someday soon will
interact with winamp.
I'm trying to send and post messages between my Delphi program and winamp.
I know Winamp's window is found using

                    hwnd_winamp = FindWindow(Winamp v1.90, Null);

I've converted  that into this code:

procedure TForm1.Button1Click(Sender: TObject);
var
    hwnd_winamp : THandle;

begin
   hwnd_winamp := FindWindow('Winamp v1.x',NiL);
      SendMessage(hwnd_winamp,WM_WA_IPC,0,IPC_STARTPLAY);
end;
end.

I know the sendmessage is written correctly to be read by winaamp, but when
I try to run my application:
WM_WA_IPC and IPC_STARTPLAY both come up as undeclared identifier errors.
 what do the need to be identified as? and are nill and null the same
thing.

Thanks in advance

Where did you get WM_WA_IPC and IPC_STARTPLAY from? They are not defined as
part of windows. Their values should be defined wherever you got them from.