Are you going from Krakow? If so allow a full day, as the tour lasts around 3 hours and there's also a short film you can watch. The journey there takes 1.5 - 2 hours on the public bus, which you can catch from the main bus station in the centre of town.
Auschwitz is a must-see for me, but be prepared, it's so sad and depressing... people burst into tears there, when they can see the horror that was made there by the Nazis
When you arrive and buy your ticket, it can be mass confusion. We found it difficult to know where we were supposed to go to meet with the English tour. Just keep asking people, who speak English, where to go and you will eventually have success. After that, the experience is very organized and profound.
I know someone who visited Auschwitz, very emotionally experience, his grandparents were killed there. I think he said he bought his tickets there.
Make sure you know the rules for visiting.
[ Edit: Edited on 06-May-2012, at 03:19 by sikkinouza ]