Private Declare Function FindWindow Lib "user32" _
  Alias "FindWindowA" ( _
  ByVal lpClassName As String, _
  ByVal lpWindowName As String) As Long
 
Private Declare Sub CloseWindow Lib "User.dll" (ByVal hWnd As Integer)
 
Private Sub Command1_Click()
 
Dim lhWnd As Long
Dim sTitle As String
 
sTitle = Text1.Text
lhWnd = FindWindow(vbNullString, sTitle)
 
If lhWnd <> 0 Then CloseWindow lhWnd: lhWnd = 0 'Überlauf
 
End Sub