there is no way that i know of in which you can disable the recieving of handwriten messages sorry...
the only way that you could stop receiving the handwriten messages from your contacts is if you did not have Tablet PC and had an earlier version of MSN messenger than 6.
the best thing i can recommend for you is to install maybe a handwriting tool yourself that way you can annoy them back.
/ 
sorry...
that way you can annoy them back.
gif 
