Apache/2.2.3 (Linux/SUSE)
Sugar Version 4.5.1d (Build 1273)
PHP: 5.1.2
MySQL client version: 5.0.18

I am trying to get a filter on a relate to field in task

In the task edit form I have a relate to field for account and contact.
If an account is selected then I want to select the contact but only contacts belonging to the account.

Can anyone help, point me in the right direction
Cheers
Jeanette