hiii try this
1)
<asp:TextBox ID="txtNumbers" runat="server"/>
<asp:FilteredTextBoxExtender ID="Numbers"
runat="server"
TargetControlID="txtNumbers"
FilterType="Numbers">
</asp:FilteredTextBoxExtender>
2)
<script language="javascript" type="text/javascript">
function intOnly(i)
{
if(i.value.length>0)
{
i.value = i.value.replace(/[^\d]+/g, '');
}
}
</script>
<asp:TextBox id="TextBox1" style="Z-INDEX: 102; LEFT: 240px; POSITION: absolute; TOP: 152px" Runat="server" onChange="intOnly(this);" onKeyUp="intOnly(this);" onKeyPress="intOnly(this);"></asp:TextBox>