Haven't heard any date when Catia will support Vista, this is a generel problem with Vista due to they only support DirectX and not OpenGL that business applications use.
It's not useless with 4gig ram, just see if you can get XP64 instead, Catia supports XP64 and there you will have an advantage with 4 gig ram.
Has anybody here heard about a date or Catia release to support Vista????