.
.
var
  Global_HookHandle : HWND = 0;
  Global_WinAmpHandle : HWND = 0;
  Global_HookInstalled : Boolean = false;

function AmpHookProc(nCode: Integer; wParam: WPARAM; lParam: LPARAM): LRESULT; stdcall;
begin
  if (wParam = IPC_SETVOLUME)
  then asm
    NOP; // Just for debugging purpose
  end;
  Result := CallNextHookEx(Global_HookHandle, nCode, wParam, lParam);
end;

function GlobalUnInstallHook:Boolean; stdcall;
begin
  //Hook aus der Hookchain entfernen
  Global_HookInstalled := UnhookWindowsHookEx(Global_HookHandle);
  if not(Global_HookInstalled)
  then begin
    Global_HookHandle := 0;
    Global_WinAmpHandle := 0;
  end;
  Result := Global_HookInstalled;
end;

function GlobalInstallHook:Boolean; stdcall;
var
  TID : DWORD; // Thread ID
  PID : LPDWORD; // Process ID -- Just for Testing with Sysinternals ProcessExplorer
begin
  Result := no;
  if (Global_HookHandle=0)
  then begin
    {$WARNINGS OFF}
    new(PID);
    TID := GetWindowThreadProcessId(Global_WinAmpHandle,PID);
    Global_HookHandle := SetWindowsHookEx(WH_CALLWNDPROCRET,@AmpHookProc, 0, TID);
    Global_HookInstalled := (Global_HookHandle<>0);
    Result := Global_HookInstalled;
    dispose(PID);
    {$WARNINGS ON}
  end;
end;

.
.

procedure TForm2.FindWinamp;
begin
  Global_WinAmpHandle := FindWindow('Winamp v1.x', nil);
  WinampRunning := (Global_WinAmpHandle<>0);
end;