You need some kind of tracking on your site, either JavaScript or Cookies would suffice but there are other ways. No way is 100% accurate but I do it this way:
1) Set up a program on your server that stores the users IP address and the tracking variable(s) passed to the program. The it forwards it to the required address using 'Location:' header. (Also delete old IP logs - say over 6 hours, after that they are completely useless)
2) Change your URL in the PPC campaign to something such as www.x.com/cgi-bin/track?source=GoogleAdWords&word=BlueWidgets&address=bluewidgets.html
3) On your shopping cart, check the log file of IP address/tracking data against the users IP address and you have a tracking system.
Not perfect, but - (1) Users don't get a JavaScript error if they are using an unexpected browser, and (2) Users can't block cookies or hit the back button when they see your site wants to set one (and some people do).
