Joost has created a Google Analytics filter that enables you to track your Google rankings — you can't specifically track the exact position of the keyword that was clicked like you can do with AdWords. But it is possible to determine the page he was on. To get the rankings in your Google Analytics reports you have to create a new filter: The title of the filter contains a 3, that's because filter 1 and 2 take care of filtering out everything else than Google Organic traffic. So yes: you also have to create a new profile to apply these filters on to be sure you don't screw up your main profile.
This filter only works for Google. if you want it to work for Yahoo and Live Search also, make sure you change the filters 1 and 2 so they accept Organic from all three of them. Then setup the filter like this: