Access Elements With Same IDs Within Multiple Forms?

Normally I would just use document.getElementById to get anything I need but here is my problem:

I have a zip code control that I load using AJAX. it has city, state, country, county and zip code. This gets loaded within a business application and at one point you can have both a bill to and ship to address forms on the screen at the same time, loading my zip control with the same fields, same ids and same name. This forced me to now pass in the form name that contains the control.

I need to get to divs and spans within this form. Primarily as you type in a city or zip code, I am doing a hot search with a popup div that shows you results you can quickly choose from. The only time this becomes an issue is the situation I mentioned before when the zip code control is on the screen twice. I am not certain how to access the innerHTML of a span or div by way of the form name. Is this possible and if so what is the proper syntax?

Here is a very basic example at its simplest form of my problem.

<form name="frm_billto" id="frm_billto">
<span id="myspan">Hello</span>
</form>
<form name="frm_shipto" id="frm_shipto">
<span id="myspan">World</span>
</form>

In the above example because the control was loaded twice, I now have 2 spans with the same ID. I want the innerHTML of the each span based on the form they are in.

We wanted one control that we could use throughout the system that we could update in one place and the entire application be updated. Unfortunately we did not anticipate having it load more than once on the page.