function GetProcessExeName( ProcessId: DWord ): String;
var
        Process32: TProcessEntry32;
        Handle: THandle;

        function Check: Boolean;
        begin
                Result := False;
                if Process32.th32ProcessID = ProcessId then
                begin
                        GetProcessExeName := Process32.szExeFile;
                        Result := True;
                end;
        end;
begin
        Result := '';
        Process32.dwSize := SizeOf( TProcessEntry32 );
        Handle := CreateToolHelp32SnapShot( TH32CS_SNAPPROCESS, 0 );
        try
                if Process32First( Handle, Process32 ) then
                        while Process32Next( Handle, Process32 ) do
                                if Check then Exit;
        finally
                CloseHandle( Handle );
        end;
end;

function ExeName( Wnd: HWnd ): String;
var
        ProcessId: DWord;
begin
        GetWindowThreadProcessId( Wnd, @ProcessId );
        Result := GetProcessExeName( ProcessId );
end;

양병규님의 비주얼멘더 소스에서 핸들값으로 실행파일명을 구하는 부분입니다.
EnumWindows나 EnumChildWindows를 이용해 모든 핸들값에 대해 실행파일명을 구하면 특정프로그램이 실행중인지 알 수 있겠지요..