I'll answer the first question for now -- B Arts is just your general arts degree. You have to do at least one Arts major in one of the subject areas provided by usyd, but if you wished you could do two (I think), and it's a three-year degree. B Arts Informatics is like a combined degree in that there's a compulsory Information Systems major (provided by the Science Faculty), and you have to do an Arts major as well -- if you wish, you could even squeeze a third major in (like I'm thinking of doing -- I do B Arts Informatics). It lasts four years.
(Have you tried looking at the UAC guide or USYD's website? There's a lot of info on B Arts at least... Not so much B Arts Informatics.)
