The times that I've been in Canberra it has been a very quiet affair. Being the capital city it is full of bureaucrats and politicians - so it doesn't have the nightlife that Melbourne or Sydney have. Weekdays most places close very early.
It does have a rather large student population at ANU (Australian National University) so I think the the campus would be a good place to start and find out about the student parties. almost 8 years ago
Good regions to head out to in Canberra are Manuka & Civic. Manuka has lots of nice restraunts, clubs, cocktail bars etc. In Civic there are are a few more pubs and clubs aimed at the student nightlife and young government employees - of which there are alot.
For the 20s 'hotspots', I'd try
Civic nightclubs: UniPub, Mooseheads, Academy, ICBM.
Kingston: Green square - Holy Grail, Filthys, Durham, Belguim Beer Cafe
Manuka: Minque, Julep Lounge, (there are more but I don't go there much, sorry)
There are plenty of other nice swish bars and clubs in Civic too (Knights Bridge, North Bar, Kremlin, Hippo Bar, Tongue & Groove) - but the ones above seem to be the busiest. almost 8 years ago