You, of course, will need equipment in order to ride. You can rent your equipment from the mountain or from a shop in the city. You can generally save a little bit of money if you rent in town but you then have the hassle of meeting deadlines to get your equipment returned.
In the Boise area there are a lot of places to rent your gear. Some of these places will also do season leases on the gear so you only have to return until the season is up. Check with places like the Newt & Harolds, Water Ski Pro Shop, McQs, and Sports Authority among others.
Renting on the mountain is convenient and easy. Any problems you may encounter with your equipment will be fixed on the spot. You will pay a little bit more but you will get quality gear and service, plus you do not have to worry about returning it in town when you are done playing.