Retrieves the handle to the top-level window whose class name and window name match
#include <WinAPISysWin.au3>
_WinAPI_FindWindow ( $sClassName, $sWindowName )
| $sClassName | A string that specifies the class name or is an atom that identifies the class-name string. If this parameter is an atom, it must be a global atom created by a call to the GlobalAddAtom function. The atom, a 16-bit value, must be placed in the low-order word of the $sClassName string and the high-order word must be zero. |
| $sWindowName | A string that specifies the window name. If this parameter is blank, all window names match. |
| Success: | The handle to the window |
| Failure: | 0, call _WinAPI_GetLastError() to get extended error information |
Search FindWindow in MSDN Library.