hi lisa,
if you want to add the sellathon counter to existing listings before july 10th you can do so manually:
sign up (if you haven't already) with this link http://v3.sellathon.com/
once signed up & logged in go to tracking code tab.
it will give you the html coding to add to your listing.
if you want to learn more about using Auctiva:
http://www.auctiva.com/help/tutorials.aspx
hope this helps!