Public Class Form1
  Const ES_NUMBER = &H2000&
  Const GWL_STYLE = (-16)
  Private Declare Unicode Function SetWindowLong Lib "user32" Alias "SetWindowLongW" _
   (ByVal hwnd As IntPtr, ByVal nIndex As Integer, ByVal dwNewLong As Integer) As Integer
  Private Declare Unicode Function GetWindowLong Lib "user32" Alias _
   "GetWindowLongW" (ByVal hwnd As IntPtr, ByVal nIndex As Integer) As Integer

  Private Sub Form1_Load(sender As Object, e As EventArgs) Handles Me.Load
    SetWindowLong(TextBox1.Handle, GWL_STYLE, GetWindowLong(TextBox1.Handle, GWL_STYLE) Or ES_NUMBER)

    Dim hwndTB As IntPtr = CType(NumericUpDown1.Controls(1), TextBox).Handle
    SetWindowLong(hwndTB, GWL_STYLE, GetWindowLong(hwndTB, GWL_STYLE) Or ES_NUMBER)
  End Sub
End Class

  Private Sub NumericUpDown1_KeyPress(sender As Object, e As KeyPressEventArgs) Handles NumericUpDown1.KeyPress
    'допустимы цифры либо возврат каретки
    Dim reg As Regex = New Regex("[0-9]")
    If (reg.IsMatch(e.KeyChar) = False) And (Asc(e.KeyChar) <> 8) Then e.KeyChar = ","
  End Sub