if the foreign income was taxed in a foreign country, then you need to be able to show this income against foreign taxes paid -- form 1116. If on the other hand , you consulted, got paid by a foreign client but did NOT pay any foreign taxes, then just convert the amount in US dollars ( using exchange rate when exchanged or anual average exchange published by the treasury, whichever is more apropo) and include in your gross income on schedule-C
