Lol Casmira don't confuse these poor sods!!
Summer Semester is basically the End of Semester 2 (Google UNSW Key dates 2008), so equivalent to Early December.
Enrolment to Summer Semester courses open during late October (an official date will be labelled at the Key Dates site closer to October).
I know it's quite confusing this year because UNSW decided to change its semesters, renaming, all for the sake of these 12 week semesters. Ignore the A or B letters that follow e.g. Semester 1, or Semester 2 or Summer Session, etc.
To make things easier, here's the Summer offering of courses in 2008:
http://www.timetable.unsw.edu.au/2008/KENSUGRDU1.html
Please note, some courses may or may not offer allocation during Summer sesson.
As for the courses, most are General Education courses (Read up on our Gen Ed FAQ if you don't know what this is, its compulsory to Single Degree ppls). While others like CHEM1011 which has a drastically high number of students failing, will be reoffered during Summer Session.