If you don't want the user to copy/cut the data from your presentation,  
don't offer a presentation of the data that would normally allow that but  
in which you've tried to disable the behavior.  First, you will annoy the  
user (frankly, this sort of thing pisses off lots of users, myself  
included).

Second (and perhaps more compelling to you), you will not succeed in  
completely disabling the behavior anyway; some user will get past your  
attempt, because the data is really there waiting to be copied from the  
presentation (the Excel spreadsheet in this case).  Filtering right-clicks  
is a really weak way to block copying (I haven't bothered to try to defeat  
the exact method you're using here, but I regularly bypass it in other  
contexts).  It is _only_ annoying, and won't accomplish what you want.  
The worst of both worlds.

If you want to present an Excel document that the user cannot copy data  
from, use Excel's application interface to copy the spreadsheet to a  
bitmap or metafile (see, for example, the Range.CopyPicture() method), and  
then present _that_ to the user.  The bitmap is more secure, but the  
metafile will perform better (use less memory...though for a reasonably  
small spreadsheet that may not matter).

In either case, it would still be theoretically possible for the user to  
copy data (bitmap would require OCR, metafile has text embedded so if the  
user can somehow get it to a tool that will extract the text, they've  
still got the data), but in both cases the effort to get at the data would  
be _much_ greater than that required to bypass whatever right-click  
filtering you attempt.  It will be simpler for the user to just get a  
screen-shot and/or hand type the data in somewhere else (to name a couple  
of techniques that you'll never be able to stop).

Doing it this way, the user also will never see something that _looks_  
like they ought to be able to select and copy and paste but can't (keeping  
in mind, of course, that if the spreadsheet is anywhere on the user's  
computer, they _can_ get to it somehow...the goal here is just to not do  
something that is so completely dumb as to require practically no effort  
to bypass but still annoy the user :) ).

And if for some reason it's important to you that the user be able to  
interact with the spreadsheet as an actual spreadsheet (select cells,  
format them, etc.) then for crying out loud, stop trying to get in the  
user's way when they want to use the context menu.

The last thing this world needs is yet another piece of software that  
presumes it has more rights to the user's data than the user has (and make  
no mistake...if the data is sitting there in front of the user, having  
been delivered to his computer, it's _his_ data now, no matter where it  
came from originally).

Pete