Activity Category

Hello All

while maintaing category for a specific activity type say TASK,is it possible to restrict the vaues of those categories at the time of transation processing;

i have created categories like ;Visit,Telephone call,Email,Preparation

Reminder

and now i want to restrict th evalues --Visit,Telephone call,Email to only activity type APPOINTMENT AND NOT FOR TASK and similarly remaining two categories for transaction type only TASK.

PLEASE LET ME KNOW WHERE CAN I DO THIS IN CUSTOMISING

Regards

Phani K