DelphiHelp.org

uses Windows; 

procedure ShowDllPath stdcall;
var
  TheFileName: array[0..MAX_PATH] of char;
begin
  FillChar(TheFileName, sizeof(TheFileName), #0);
  GetModuleFileName(hInstance, TheFileName, sizeof(TheFileName));
  MessageBox(0, TheFileName, 'The DLL file name is:', mb_ok);
end;