Text To URL In New Window

I'm trying to write a script that will take text from 2 fields in a form and convert them into a url that is then launched in a new window, via a button click. Here's what I have which obviously doesn't work!

<script> function convertURL() {
var zip5 = document.getElementsByName( "zip5")[0];
var zip4 = document.getElementsByName( "zip4")[0];
var fullurl = document.getElementsByName( "fullurl")[0];
var urlparts = document.getElementsByName( "urlparts")[0];
[Code]....