I have been advised to update my aperture software from 3.2.2 to 3.4.3. Not having a clue, how does this affect my projects in the old version?
Well, it shouldn't really affect them. Note your library will be upgraded as part of the software upgrade, to a format which is incompatible with older versions of Aperture. So you'll need to update all your copies of Aperture if you have more than one computer.
Also, HAVE AN UP TO DATE BACKUP before you do this. A Time Machine backup AND an up-to-date vault would be good.