On the MLS, it should state what the commission will be in the commission field. Typically it is anywhere between 25% to 50% of the 1st month's rent, though I've seen it both lower and higher. Some times I have had success getting non-MLS rentals to give a commission too. As Patrick says, Ask! As far as the commission being paid to you, the money should be paid to your broker, as is a commission for the sale of a listed house. The broker usually will take the percentage you have agreed on as your split and then give you a check for the remaining balance.

The listing should have a payout listed on the listing. If not, ask for one.