You should be able to compare the fields in your backing bean's action method itself. By the time the action method is called, the password and the verify password fields will already be posted to the backing bean and they will be available for your validation.
After comparing, if it fails your validation, you may choose to redisplay the same page with a message:
Make sure you are using h:messages in order to display this message.
I think there is also another approach to do a combined field validation. In this approach, you should have a dummy hidden field AFTER all your fields that need combined validation. This hidden field should have a validator attribute which will call the validation method of your backing bean.