Class Form1
 
  Dim dragRec As Boolean, mPos As Point
  Dim Rect As New Rectangle(80, 45, 160, 90)
 
  Private Sub pb1_MouseDown(sender As Object, e As MouseEventArgs) Handles _
    PB1.MouseDown
    If e.Button = MouseButtons.Left AndAlso Rect.Contains(e.Location) Then
      dragRec = True
      mPos = e.Location
      TB1.Text = mPos.ToString
    End If
  End Sub
 
  Private Sub pb1_MouseMove(sender As Object, e As MouseEventArgs) Handles _
    PB1.MouseMove
    If Not dragRec Then Exit Sub
    Dim p As Point = Rect.Location + (e.Location - mPos) 'neue Rechteck-Position
    mPos = e.Location 'aktuelle Mausposition merken
    If p.X < 0 Then p.X = 0
    If p.Y < 0 Then p.Y = 0
    If p.X + Rect.Width > PB1.Width - 3 Then p.X = PB1.Width - 3 - Rect.Width
    If p.Y + Rect.Height > PB1.Height - 3 Then p.Y = PB1.Height - 3 - Rect.Height
    If p <> Rect.Location Then
      Rect.Location = p
      PB1.Refresh()
    End If
  End Sub
 
  Private Sub pb1_MouseUp(sender As Object, e As MouseEventArgs) Handles _
    PB1.MouseUp
    dragRec = False
  End Sub
 
  Private Sub pb1_Paint(sender As Object, e As PaintEventArgs) Handles PB1.Paint
    e.Graphics.DrawRectangle(Pens.Red, Rect)
  End Sub
 
End Class