Limit the transaction types by role

Hi experts,

We´re involved in a SAP CRM implementation. We´d need to know if it´s possible to link Transaction Types with a Business Role. This is, when the user goes to create a new task, a window pops up with all tasks: is it possible to limit Tasks by Business Role? Maybe there´s a customizing point where you can define, by business role, the availabe tasks for that business role.

Thanks in advance.

Javier