El siguiente código hace eso, aunque asumiendo que todas las sesiones de Excel tengan el título por defecto, es decir, "Microsoft Excel - ....", mejor dicho, que no se haya modificado la propiedad
Application.Caption
Necesita Excel 2000 o superior, por el operador AddressOf.
<font face=Courier New><SPAN style="color:#00007F">Option</SPAN> <SPAN style="color:#00007F">Explicit</SPAN>
<SPAN style="color:#00007F">Declare</SPAN> <SPAN style="color:#00007F">Function</SPAN> EnumWindows <SPAN style="color:#00007F">Lib</SPAN> "user32" (<SPAN style="color:#00007F">ByVal</SPAN> lpEnumFunc <SPAN style="color:#00007F">As</SPAN> <SPAN style="color:#00007F">Long</SPAN>, _
<SPAN style="color:#00007F">ByVal</SPAN> lParam <SPAN style="color:#00007F">As</SPAN> <SPAN style="color:#00007F">Long</SPAN>) <SPAN style="color:#00007F">As</SPAN> <SPAN style="color:#00007F">Boolean</SPAN>
<SPAN style="color:#00007F">Declare</SPAN> <SPAN style="color:#00007F">Function</SPAN> GetWindowText <SPAN style="color:#00007F">Lib</SPAN> "user32" Alias "GetWindowTextA" _
(<SPAN style="color:#00007F">ByVal</SPAN> hwnd <SPAN style="color:#00007F">As</SPAN> <SPAN style="color:#00007F">Long</SPAN>, <SPAN style="color:#00007F">ByVal</SPAN> lpString <SPAN style="color:#00007F">As</SPAN> <SPAN style="color:#00007F">String</SPAN>, <SPAN style="color:#00007F">ByVal</SPAN> cch <SPAN style="color:#00007F">As</SPAN> <SPAN style="color:#00007F">Long</SPAN>) <SPAN style="color:#00007F">As</SPAN> <SPAN style="color:#00007F">Long</SPAN>
<SPAN style="color:#00007F">Declare</SPAN> <SPAN style="color:#00007F">Function</SPAN> GetWindowTextLength <SPAN style="color:#00007F">Lib</SPAN> "user32" Alias "GetWindowTextLengthA" _
(<SPAN style="color:#00007F">ByVal</SPAN> hwnd <SPAN style="color:#00007F">As</SPAN> <SPAN style="color:#00007F">Long</SPAN>) <SPAN style="color:#00007F">As</SPAN> <SPAN style="color:#00007F">Long</SPAN>
<SPAN style="color:#007F00">'Variable que tiene el número de sesiones</SPAN>
<SPAN style="color:#00007F">Dim</SPAN> Counter <SPAN style="color:#00007F">As</SPAN> <SPAN style="color:#00007F">Long</SPAN>
<SPAN style="color:#00007F">Private</SPAN> <SPAN style="color:#00007F">Function</SPAN> EnumWindowsProc(<SPAN style="color:#00007F">ByVal</SPAN> hwnd <SPAN style="color:#00007F">As</SPAN> <SPAN style="color:#00007F">Long</SPAN>, <SPAN style="color:#00007F">ByVal</SPAN> lParam <SPAN style="color:#00007F">As</SPAN> <SPAN style="color:#00007F">Long</SPAN>) <SPAN style="color:#00007F">As</SPAN> <SPAN style="color:#00007F">Boolean</SPAN>
<SPAN style="color:#00007F">Dim</SPAN> sSave <SPAN style="color:#00007F">As</SPAN> <SPAN style="color:#00007F">String</SPAN>, Ret <SPAN style="color:#00007F">As</SPAN> <SPAN style="color:#00007F">Long</SPAN>
<SPAN style="color:#007F00">'Texto de la ventana</SPAN>
Ret = GetWindowTextLength(hwnd)
sSave = Space(Ret)
GetWindowText hwnd, sSave, Ret + 1
<SPAN style="color:#007F00">'Comparar el texto de la ventana con el que se asume, "Microsoft Excel"</SPAN>
<SPAN style="color:#00007F">If</SPAN> InStr(1, sSave, "Microsoft Excel", 1) > 0 <SPAN style="color:#00007F">Then</SPAN>
Counter = Counter + 1
<SPAN style="color:#00007F">End</SPAN> <SPAN style="color:#00007F">If</SPAN>
<SPAN style="color:#007F00">'Continuar</SPAN>
EnumWindowsProc = <SPAN style="color:#00007F">True</SPAN>
<SPAN style="color:#00007F">End</SPAN> <SPAN style="color:#00007F">Function</SPAN>
<SPAN style="color:#00007F">Public</SPAN> <SPAN style="color:#00007F">Sub</SPAN> CountInstances()
Counter = 0
EnumWindows AddressOf EnumWindowsProc, <SPAN style="color:#00007F">ByVal</SPAN> 0&
MsgBox Counter
<SPAN style="color:#00007F">End</SPAN> <SPAN style="color:#00007F">Sub</SPAN>
</FONT>
Este texto lo modifiqué a partir de un ejemplo de
www.allapi.net
