How can i use the remote from my yamaha rx-v465 reveiver to control the scientific atlanta 8300hb cable box?

Yamaha remote has ability to control other devices (TV, DVD, cable box, ...) only by pre-defined set of models. Look up in your manual to the Yamaha where you will find list of manufacturers and models of devices with corresponding codes. If you can find your model there, program it into the remote. If not, you can try some of the other codes, at least program +/- and other simple functions should be quite compatible among brands.