stimpy, in most cases Americans cannot do business in Iran or with Iranian nationals. Travel is a different matter -- there's no travel ban a la Cuba here. From http://www.ustreas.gov/ofac/t11iran.pdf :

All transactions ordinarily incident to travel to or from Iran, including the importation of accompanied baggage for strictly personal use, payment of mainte-nance and living expenses and acquisition of goods or services for personal use are permitted.