Receiveing a check from overseas, the amount not always equal to the amount due because of the exchange rate, how can I count for the difference in the book.

yes the rate would always affect the amount.

the difference would be accounted for as gain/loss on foriegn currency translation.

if the current amt is higher than what is recorded, then it would be a gain. if it is lower, then a loss would be recorded on the date of exchange.