Hope any JavaScript programer can help me with this question, cuz I don't know anything about it.

I have a simple computer quote script, I put example here:

<script language=javascript>
var called=false;
var T_Price=0;
var memory_flag;
var cpu_flag;

function compute(form){

if (form.cpu[0].selected){cpu_flag= 0;cpu_print="None";}
if (form.cpu[1].selected){cpu_flag= 69;cpu_print="AMD K6-2-500Mhz $69";}

if (form.memory[0].selected){memory_flag=0;memory_print="None";}
if (form.memory[1].selected){memory_flag=29;memory_print="32MB PC100 SDRAM $29";}


My question on the memory on the HTML section, I want to put a drop down quatity box in the memory section. How can I do that to trigger the calculate forum, please give me the details as I don't have any javascript programing knowledge, thanks a lot.