function numbersonly(e)
{
var keynum;
var keychar;
var numcheck; 

if(window.event) // IE
{
keynum = e.keyCode;
}
else if(e.which) // Netscape/Firefox/Opera
{
keynum = e.which;
}

keychar = String.fromCharCode(keynum);
numcheck = /\d/ ;

return numcheck.test(keychar) || keynum == 13;
}