Thanks to everybody for the answers and the info provided!
I have another question: how much does it cost to have the Internet per month in Thessaloniki?
@Savvy?!: 300 Euro for two rooms and a kitchen is really cheap and sounds great. Does this price include electricity, water and other bills? It would be great if I find something like that. The AUTH administration gave me a double room at 134 Kassandrou Str (that's very near AUTH) that has a bathroom and a kitchenette for 210Euro per month. I hope it will be OK. The only inconvenience is that the bed is a bunk bed
If somebody from the forum is willing to rent an apartment/room etc with me, write a personal message pls. If we find something better than the dormitories, we could rent it for the semester.
@marigitte: Do not worry about your English, you're coming to improve it, so study hard and you won't have problems. The reason I chose Greece is because I want to improve my Modern Greek. I'm intermediate now and I hope that after a semester I'll speak it very well.
@gosia: I don't know anybody from my university that's going to ATEI. Why don't you ask them to give you some other students' contacts?
@driver: Thanks for the link. Do you have anything to do with that profile?