I am also interested to learn how sales are tracked. My boss has separate landing pages for his Overture search terms. Is he on the right track? How can he subsequently determine that the pages are the first step in a completed sale?
Some people track results with a high degree of specificity by setting up affiliate software, and giving each PPC term its own affiliate link. This would let you track things through from click to conversion. This could also track results of emails, joint ventures etc.. Look for affiliate software that generates short, "pretty" referral links based on your own domain name.