Hello
I have spent about 6 weeks in Warsaw this year and it surprises me how bad the Polish youth is at English in general.
It's true that English is known on a rather mediocre level in Poland among youth (although there is a lot of exceptions from it), but at least the knowledge of English among Polish youth is very common (actually there are very VERY little young people who don't know any English) and it's rather hard to find someone who don't understand a word.
I've never studied in Warsaw co I can't help you concerning your studies, but on a other note I've studied in Krakow and saw and met a lot of foreign students and can assure you that you don't have to know any Polish in the big cities (smaller one's is a different tale) to easily communicate, in most cases only English is more than enough, and if not English then German or Russian could sometimes do.
With Regards.