Recently at my job, I had to setup Bronto email tracking pixels on our order confirmation page. The tracking pixels came in the form of an image tag and had to be populated with some values from our shopping cart. The values (invoice number and order amount) are passed from the order confirmation page using hidden fields.
<input name="InvID" type="hidden" id="InvID" value="12345" />
<input name="Tot" type="hidden" id="Tot" value="69.9900" />
var InvoID = document.getElementById("InvID").value;
var SubTotal = document.getElementById("Tot").value;
I have recently found that if you have apostrophes in your code, it will break the above tracking script. A way around this would be to use a string replace function like this:
*NOTICE: The values in the scripts are dummy values, as I had to hide some confidential account data. The code is just to show as an example, but its pretty easy to setup. You can use similar techniques to setup Google, MSN, Yahoo, and other types of tracking pixels.