PHP tracking script needed

Hello, I need a PHP tracking script for my website, that is available to track keywords which the visitors came from, and insert the keyword at the subID variable of the affiliate link. At the same time the affiliate links must be hidden. Here is an example: Visitor comes from: [login to view URL];ie=utf-8&oe=utf-8&aq=t&rls=[login to view URL]:bg:official&client=firefox-a Keyword is "money" Then visitors leaves through my affiliate link, which is like this one: [login to view URL];s=yy&ck=site1&kw={$kw} The {$kw} is a variable. I want the script to be able to take the word money, and put it on the place of the variable {$kw}. At the same time I want my affiliate not to be visible. Currently they are hidden by the PHP redirect method. It is not a problem if the script needs other redirecting method. If anyone is capable of making such script - contact me for any information that you may need. I'm not sure what the price should be, but I think this is not a hard task for good coders, so I expect reasonable price for the service. I'd also like to be capable of trying the script by myself before purchasing it (if possible) - something like demo version.