go to your user's and cut their hands off !!
there's no way to disable it, especially NOT in javascript !!
(actually, you can either use some kind of a custom ie by modifying CLIENT reg's key with vc++; or open a sub window without the bar, but still the right click can be used ... you can disable the right click, but still, ... and so on )
but as a user, if you'd use any of those solutions, i mean, if you try to force ME to use the web YOUR way, i won't come anymore to your site ... and i'm not the only one ...
please check for "how to disable view source" issues in this forum, all these (that you can ... but that there is ALWAYS a workaround, and that anyway it's useless as you're supposed to design for USERS and not for you/your boss) are quite well explained