TextBox1.Attributes.Add("onKeyPress", "return goodchars(event,'0123456789')")

<SCRIPT TYPE="text/javascript">

function getkey(e)

{

if (window.event)

return window.event.keyCode;

else if (e)

return e.which;

else

return null;

}

function goodchars(e, goods)

{

var key, keychar;

  key = getkey(e);

if (key == null) return true;

// get character

  keychar = String.fromCharCode(key);

  keychar = keychar.toLowerCase();

  goods = goods.toLowerCase();

// check goodkeys

if (goods.indexOf(keychar) != -1)

return true;

// control keys

if ( key==null || key==0 || key==8 || key==9 || key==13 || key==27 )

return true;

// else return false

return false;

}

</SCRIPT>