Hi,
there can be many reasons why the Powerpoint file causes Notebooks to crash. One is that the current version of Notebooks is not yet certified for iOS 4.2 (although we do not expect to see many issues here).
It is more likely that the ppt file itself is too big or requires too much memory and the iOS simply shuts down Notebooks; in the case, there is little we can do.
Since you have already installed iOS 4.2GM I suppose that you are an "advanced" iPad user. Would you mind taking a look at the crash reports and see what is documented as the reason?
Thank you,
Alfons