My first two trips I used Magnum Belize tours at www.magnumbelize.com
they were wonderful. Now I book my own with the hotel/resort and the airlines, and it worked just great.
Booking with the hotel/resort you will need to do by email, and then fax them a photo copy of your credit card and driver's license. But be aware of that resort's cancellation policy. If you need more help come back here. Belize IT