Class Form1
  Dim dragRec As Boolean
  Dim 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 Rect.Contains(e.X, e.Y) Then
      Cursor.Current = Cursors.Hand
    Else
      Cursor.Current = Cursors.Default
    End If
 
    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

Option Strict On
 
Class Form1
 
  Dim Rect As New Rectangle(80, 45, 160, 90) 'Rechteck
  Dim Diff As Size 'angeklickte Differenz
  Dim DragRect As Boolean 'Maustaste gedrückt
 
  Private Sub PB1_MouseDown(sender As Object, e As MouseEventArgs) Handles _
    PB1.MouseDown
    If e.Button = MouseButtons.Left AndAlso Rect.Contains(e.Location) Then
      Diff.Width = e.X - Rect.X
      Diff.Height = e.Y - Rect.Y
      DragRect = True
    End If
  End Sub
 
  Private Sub PB1_MouseMove(sender As Object, e As MouseEventArgs) Handles _
    PB1.MouseMove
    If Rect.Contains(e.Location) Then
      Cursor.Current = Cursors.Hand
    Else
      Cursor.Current = Cursors.Default
    End If
 
    If Not DragRect Then Exit Sub
 
    ' Position berechnen
    Rect.Location = e.Location - Diff
 
    ' Rechteck begrenzen
    If Rect.X < 0 Then Rect.X = 0
    If Rect.Y < 0 Then Rect.Y = 0
    If Rect.X + Rect.Width > PB1.Width - 3 Then Rect.X = PB1.Width - 3 - _
      Rect.Width
    If Rect.Y + Rect.Height > PB1.Height - 3 Then Rect.Y = PB1.Height - 3 - _
    Rect.Height
 
    ' neu zeichnen
    PB1.Invalidate()
  End Sub
 
  Private Sub PB1_MouseUp(sender As Object, e As MouseEventArgs) Handles _
    PB1.MouseUp
    DragRect = 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