Ah, this is a pesky problem. Utilizing help from various sources, I banged my head for quite awhile about a year ago and came up with something that worked... almost. In my example, the right click is replaced, rather than disabled. I made it produce a DHTML right-click menu that controls the Flash movies navigation.
The problem: It only works on transparent areas of the Flash movie. If you click on the gray, the typical menu appears. ####, it was frustrating. You've probably seen the effect before. It's been done by others.
http://www.networksplus.net/sem/Back-RightClick/index2.html
I did find someone who has a method that blows my sorry (and overdone) attempt out of the water. It utilizes inline frames and is only good in IE5+ (maybe NS6 now). There are instructions for disabling right click altogether if I remember right. Rather than blather on, here's the link. You might want to check it out:
http://www.instantflash.com/rightclick/
(Edited by Sem at 10:43 pm on Feb. 17, 2002)