You are not a citizen until you are sworn in. If you are denied because of failure to pass the English or the civics test, you will be automatically rescheduled within 90 days. If you are not approved for some other reason, you may be given time to overcome the problem.
For 2009, the American Opportunity Credit--which is a variation of the Hope Credit--will be allowed for 4 years. For years before and after the new credit is allowed, the Hope credit is supposed to be for 2 years.
To claim the American Opportunity Credit, the student must be in the first four academic years of postsecondary education at an eligible school. It doesn't matter how many calendar years the student has been in school, as long as he or she is in still the freshman, sophomore, junior, or senior year.