//makes sure that only numbers 0123456789 are entered into the field.
function isDigit(what){

		InString=what.value;
		entry=what.name;

        RefString="1234567890";
        for (Count=0; Count < InString.length; Count++)  
        {
                TempChar= InString.substring (Count, Count+1);
                if (RefString.indexOf (TempChar, 0)==-1)  
                {
                        alert("Please enter numbers only (0123456789).");
                        what.focus();
                        what.select();
                        return false;
                }
        }
        return true;
}