Option Explicit

Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long
Private Declare Function GetClientRect Lib "user32" (ByVal hwnd As Long, lpRect As RECT) As Long

Private Type RECT
    Left As Long
    Top As Long
    Right As Long
    Bottom As Long
End Type

Function a()
Dim hwnd As Long
Dim Rectangle As RECT

hwnd& = FindWindow("Shell_TrayWnd", "")

    GetClientRect hwnd&, Rectangle
    MsgBox "Ancho : " + Str$(Rectangle.Right - Rectangle.Left) + " Pixels." + Chr$(13) + "Alto : " + Str$(Rectangle.Bottom - Rectangle.Top) + " Pixels."

End Function