How to setup a Router to do Dual Wan

I have a routerboard 133 os ver 2.9.83 I wish to do a dual wan w/load balancing on this router. How could I accomplish this? One wan connection would be coming from a Adtran unit that has 3Mbs bonded T1 with static and the other wan connection would be a cable modem or DSL modem with a either a dhcp or static ip.

try to search:
http://forum.mikrotik.com/search.php?st=0&sk=t&sd=d&keywords=load+balancing
or
http://wiki.mikrotik.com/wiki/Load_Balancing_over_Multiple_Gateways