This information might be useful not only for those who come to our winter course which starts next monday, but also future courses, seminar and individual classes in Warsaw.
Especially if there come several people together, very good alternative to hostel or hotel could be renting an apartment for a few days (or even one night).
Here are two of internet services through which you could book an apartment for short periods of stay.
http://dobranoc.eu/index.php?page=angielski - it's in English and Polish
http://www.noce.pl/SR/index.php?lang=en - this one helps to book apartment not only in Warsaw, but also in other cities in Poland, and is in English, German, Italian, Russian, French, Spanish and Polish.