Conference accomodation
The closes to PIAP is hotel Czerniewski which is 15 minutes walk form PIAP.
Unfortunately their web page doesn't work, but you can send an email directly to recepcja@hotelczerniewski.pl
However, the best way is to book the room via booking.com service
http://www.booking.com/hotel/pl/czerniewski.pl.html
You can also book any hotel in Warsaw using booking.com service, if you require location, which is closer to the city centre or to the Old Town.