Tracking key words that generate sales

How do you track which key words generate sales?

[Bio4ce]

How can I track which key words actually generate sales? I know what is necessary to calculate ROI. The major problem I'm having is finding out which terms generate sales. My last campaign was October/November and that was my major problem in evaluating the success of each of the terms I bid on. I always knew when someone had come to my site. I knew when a sale was made. I just never knew what terms resulted in those sales. My hosting site uses AW Stats, Webalizer, and Analog stats. All of these are pretty basic.

Are there any good recommendations on how to do this? I don't want to put in a lot of JS on my pages to track visitors. Anything simple?

Thanks.

:)

<added>

Just to be clear, I want to determine the ROI on each term, not just the campaign as a whole. Thanks.

[gsx]

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).