A few weeks ago it was decided that Non-BB topics would be allowed in the regular forums. So this is now BB as well as non-BB.
As Snow says: take the bike. If you're gonna stay here for 6 months you should just a cheap bike and a good extra lock (only 1 regular lock means it'll get stolen). As an Erasmus student you probably got housing arranged already and you can probably cook there, which helps you meet the other Erasmus students as well. In amsterdam each house with international students has a few dutch students that are in charge and arrange stuff that you can do. So they can probably help you as well if you have questions.
I personally don't know Groningen that well, but I guess some people here will have good tips for bars and food.
Enjoy your time in Holland.
Crunchy! If you eat fast enough