Adding Text Field That Insists On Numeric

I'm trying to add a text box to a form that has some other complications. My "mcomment" in the code below does work but will only accept numbers, and the whole idea was text.

Code:
function n_od(type) {
var f = document.forms.create_account;
$("#id_od").html("<img src='images/nr_loading1.gif' border=0>");
subcat3 = escape($("#subcat3").val());
if (type == 2)
$("#id_od").load("n_autos.php?step=115&w="+f.width.value+
"&fractionw="+$("#fractionw").val()+"&length_in="+f.length_in.value+
"&fractionl="+$("#fractionl").val()+"&mcomment="+f.mcomment.value+
"&mcat="+$("#mcat").val()+"&subcat="+$("#subcat").val()+"&subcat3="+subcat3);
else {
$("#id_od").load("n_autos.php?step=116&w="+f.width.value+"&fractionw="+
$("#fractionw").val()+"&length_in="+f.length_in.value+"&fractionl="+
$("#fractionl").val()+"&mcomment="+f.mcomment.value+"&mcat="+$("#mcat").val());
}
}