Help with unstable navigation specially in I.E

Sorry to be dumb. I am new-ish. I am trying to do this site at but am having problems with the nav - bounces round and has gaps - specially with I E. I think it’s a float thing but don’t know what. I used CSS & HTML. Any clues, hints or codelinks? Also anyone know anyone who can walk me through wordpress or joomla or any good cms system? Thanks