These are trainers:
http://www.bikesomewhere.com/images/...MAGCONCEPT.jpg
They are great for indoor bike training, however they get boring quickly and they make you lazy (as you don't have to steer or balance.
These are rollers:
http://www.bikyle.com/images/EliteParbolicRoller.jpg
Rollers force you to balance, steer as well as the standard pedaling you do on a trainer... it's better for training as you don't get lazy and just pedal. It forces you to balance yourself and steer properly. The downside is that it's a bit dangerous as you can fall off and it's got quite a learning curve in getting on and getting started.