Currently our users have to check the 'public' checkbox after the email is sent.  (task) This step being forgotten, and our users can't see each others' emails.   I was told a trigger would be needed. I am not a developer and have never written a 'trigger'.  

 I would like to be able to have an error pop up when a user tries to close a case when there are open acitivities. Standard case validation rules can't be written due to the Activity object being a child object.  Can someone help use out with an apex trigger?

This would be in addition to our current related list notes/attachments. We are just starting to use VF pages, we'd apprecate any help. This new section would be for a specific tax document.