This a quick summary of a more elaborate post about using Google Analytics to measure the performance of an advertising campaign. There are two steps to setup Analytics so that it can distinguish traffic based on ad version:

1) In the link from your ad to your site, add a “utm_campaign” field like this: www.mysite.com/landing-page.php?utm_campaign=yourcampaignID

2) The “Traffic Sources.Campaigns” area in Analytics will now show data for traffic landing at that URL

You can also use this Google Tool for adding yet more Analytics fields to your URL.