How to create Component class in asp.net

Hi dear.,
 
May i know how to create Component class in asp.net.i was used the following code in VB.net but inASP.net there is no Componentclass file in
Add->Newitem
(will you please help me how to create textbox with only your can enter numbers only)
My code to create text that only accept Number and also some color change.................
 
Public Class ZillisisNumberTextBox
    Inherits TextBox
 
    Private Sub ZillisisNumberTextBox_Enter(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Enter
        Try
            Me.BackColor = Color.LemonChiffon
            Me.Font = New System.Drawing.Font("Verdana", 8.75!, System.Drawing.FontStyle.Bold, System.Drawing.GraphicsUnit.Point, CType(0, Byt ...