multivalue

My goal is to give users the option of sending out notifications to other users of specified roles when they create a certain type of node. My current (not working) approach was to create a CCK text field configured to show check boxes (there are four options) on the node creation page, then use rules to catch the check boxes and send emails.

The CCK text field is called 'field_notify', with allowed values of 'group 1', 'group 2', 'group 3', and 'group 4'.

Rule set up:
ON After Saving New Content
IF Created content is Member Post

Does anyone here have experience creating multivalue/compound CCK text-fields? I'm trying to create one and so far it seems you either have to a) make your own cck component or b) use Form API. Any advice would be much appreciated.