Ad tracker

Hello, I have an AD Tracking script and need to fix a couple of things. 1. I have to place the code on a page (for example the Home Page) and the confirmation page. Let's say that someone finds my site using Google. When they enter the page where I put the code, I can see the statistic page of that AD showing me where they came, for example I can see this: [login to view URL];start=0&start=0&ie=utf-8&hl=it&oe=utf-8&client=firefox-a&rls=[login to view URL]:it-IT:official This tells me that I got a visit from [login to view URL] with the keyword hosting2000. Now if this visitor buys one of my services and reach the confirmation page I can only see under Today's Sales column 1 telling me that I got 1 sale but I want to see were did I get that new client. If I get 100 visitors a day and make 1 sale I need to know from which search engine I got that new client and what keyword he used. I think its not difficult to do this because the scripts shows the exact URL when the visitors enter my site the first time like the [login to view URL] example above. 2. I have a shopping cart script and it creates a dynamically generated page as the confirmation page but when I put the code in the perl file of the shopping script I always get a 500 server error. Thanks