No visa is required if you come from an EU/EFTA member country or other country listed by the Polish Ministry of Foreign Affairs.
Citizens of other countries who wish to work/ study in Poland are required to obtain a Polish visa (Type: 06 – work purpose, D – multiple-entry) prior to their arrival.
They should contact the Polish Consulate or Embassy in their country of residence.
Visa is granted for maximum six months. In order to extend the stay in Poland, it is necessary to apply for a residence permit for specified period of time in a Voivodeship office. The procedure lasts 3-6 months, so one should apply as soon as possible after arrival.
All information about visa and resident permit can be found here.
They offer quite comfortable rooms at good price.
If you are coming with your family please do not forget to check the information about Visas or Residence Permit for them (section 1).
More information about Family issues? In section Additional/useful Information.