function numbersonly(myfield, e)
{
var key;
var keychar;
var fieldvalue = myfield.value+'';

if (window.event)
   key = window.event.keyCode;
else if (e)
   key = e.which;
else
   return true;
keychar = String.fromCharCode(key);

// control keys
if ((key==null) || (key==0) || (key==8) || 
    (key==9) || (key==13) || (key==27) )
   return true;

// numbers
else if ((("0123456789.").indexOf(keychar) > -1))
	{
// cannot have two periods
	if ( (fieldvalue.indexOf(".")> -1) && ((".").indexOf(keychar) > -1) )
		return false;
	else
		return true;
	}
else
   return false;
}