If you believe intel, they say that more than one celeron cannot be used in a system, they made them this way intentionally. This may just be propaganda, so try it if you can get a hold of 2 same clock speed celerons and a dual p2 board. You can never truley know until you try something yourself.
Another thing, unless you are running windows NT, dont bother with the dual board, your apps/games/os will not even see the other processor there. Good luck, and post your results, I am curious to see what will hapen.