The 8 -Digited Numeric TextBox with VB.NET:

Public Class Form1
Inherits System.Windows.Forms.Form

#Region " Windows Form Designer generated code "

Public Sub New()
MyBase.New()

'This call is required by the Windows Form Designer.
InitializeComponent()

'Add any initialization after the InitializeComponent() call

End Sub

'Form overrides dispose to clean up the component list.
Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
If disposing Then
If Not (components Is Nothing) Then
components.Dispose()
End If
End If
MyBase.Dispose(disposing)
End Sub

'Required by the Windows Form Designer
Private components As System.ComponentModel.IContainer

'NOTE: The following procedure is required by the Windows Form Designer
'It can be modified using the Windows Form Designer.
'Do not modify it using the code editor.
Friend WithEvents TextBox1 As System.Windows.Forms.TextBox
Friend WithEvents Label1 As System.Windows.Forms.Label
Private Sub InitializeComponent()
Me.TextBox1 = New System.Windows.Forms.TextBox()
Me.Label1 = New System.Windows.Forms.Label()
Me.SuspendLayout()
'
'TextBox1
'
Me.TextBox1.Location = New System.Drawing.Point(80, 72)
Me.TextBox1.Name = "TextBox1"
Me.TextBox1.TabIndex = 0
Me.TextBox1.Text = ""
'
'Label1
'
Me.Label1.AutoSize = True
Me.Label1.Font = New System.Drawing.Font("Microsoft Sans Serif", 9.75!, System.Drawing.FontStyle.Bold, System.Drawing.GraphicsUnit.Point, CType(0, Byte))
Me.Label1.Location = New System.Drawing.Point(48, 40)
Me.Label1.Name = "Label1"
Me.Label1.Size = New System.Drawing.Size(164, 15)
Me.Label1.TabIndex = 1
Me.Label1.Text = "8 digited numeric Textbox"
'
'Form1
'
Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
Me.ClientSize = New System.Drawing.Size(292, 266)
Me.Controls.AddRange(New System.Windows.Forms.Control() {Me.Label1, Me.TextBox1})
Me.Name = "Form1"
Me.Text = "Form1"
Me.ResumeLayout(False)

End Sub

#End Region

Private Sub TextBox1_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles TextBox1.KeyPress
Dim str As String = TextBox1.Text

If e.KeyChar.IsLetter(e.KeyChar) Then
e.Handled = True
End If

If e.KeyChar.IsPunctuation(e.KeyChar) Then
e.Handled = True
End If
If e.KeyChar.IsSymbol(e.KeyChar) Then
e.Handled = True
End If

If Asc(e.KeyChar) >= 48 And Asc(e.KeyChar) <= 57 Then
If str.Length = 8 Then
e.Handled = True
MessageBox.Show("Atmost 8 Digited Number are allowed")
End If
End If

End Sub
End Class