I am a non-EU citizen (Albania), living in Greece with a residence permit, in February 2016 I want to visit Poland for ERASMUS programm studies. Can I go there without a visa and stay there more than 3 months becouse the semester lasts 6 months?
No. You definitely need a type D visa (national visa) if you want to stay in other Schengen countries for more than 3 months. I am a citizen of Azerbaijan doing PhD in Germany. As part of the program, I needed to spend 1 year in Poland. Although I had 3 years of residence permit, I still needed to apply for a national visa of Poland.