The metro is the easiest and fastest way to get to Aula Magna: from the city center you take the red line towards Mörby centrum and get off at the stop called Universitetet. From there you walk about 100 meters straight ahead, past Picnic and you will find Aula Magna on the right side. From T-Centralen to the University it is about a 10 minutes ride.
You can also get to Aula Magna by bus 50, get off at Universitetet Norra and follow the same directions as above. From T-centralen to the University it is about a 30 minutes ride.
You can plan your trip at http://sl.se/en/.
Depending on when you arrive to Stockholm there are different tickets you can get. It is possible to buy single tickets for 36 SEK, but a 72 hour pass for 230 SEK is probably the most economic option if you plan to do some sightseeing in the city as well. This pass works on the metro and buses.
If you take a taxi to the University the address is Frescativägen 6.
For those attending the gala dinner at Filmhuset you may take the red line in the metro as well, but the one running to Ropsten which is the opposite direction from the University. Get off at Karlaplan and exit towards Valhallavägen, take a left and walk a few hundred meters and turn left again when you reach the roundabout. The visiting address is Borgvägen 1-5. http://www.sfi.se/en-GB/The-Film-House/System1/Global-menu/Find-us/