What type of filters is he looking for. Since it's a shared folder, my first recommendation would be to customize the Views for the specific folder. These changes would apply on an individual basis, whereas rules would affect everyone that uses the folder.

I actually need two filters which apply to all users.

The first filter should move junk e-mail to the trash folder and the second filter should show an alert whenever a fax message arrives (a message with [fax message] in the subject field).

Kind regards

Pongy