Private Sub Form_Resize()
 
  Dim MinBreite!, MinHoehe!, TwX!, TwY!
 
  If Me.WindowState = vbMinimized Then Exit Sub
  MinBreite = 400 ' Pixel
  MinHoehe = 300 ' Pixel
  TwX = Screen.TwipsPerPixelX
  TwY = Screen.TwipsPerPixelY
  If Me.Width < MinBreite * TwX Then Me.Width = MinBreite * TwX
  If Me.Height < MinHoehe * TwY Then Me.Height = MinHoehe * TwY
 
End Sub

Gruss,

Zardoz