https://adwords.google.com/support/bin/answer.py?answer=14816?ctx=awblog&sourceid=awo&subid=us-et-awb-020606_4
The best method of tracking specific clicks is to use a unique Destination URL for your keywords. A simple way to do this is often to add some URL parameters.
The ValueTrack tag is a simple tag that you can add to your Destination URLs. It will allow you to distinguish the clicks you receive from search and content sites in the Google Network. It can be used with both keyword-targeted and site-targeted campaigns. For example, if your URL is www.yoursiteinfo.com, you can use the following tag for your Destination URL:
www.yoursiteinfo.com?type={ifsearch:GoogleAdWordsSearch}{ifcontent:GoogleAdWordsContent}