Maps and directions to the Polytechnique campus can be found here.
From the airports, you should count 1h30 from Roissy and 30 mins from Orly by public transportation. For those in a hurry, a taxi trip will cost about 90€ (35€) and take 1h (20mins) from Roissy (Orly).
Additional documents:(also on the front page)
Ile-de-France Public transportations search portal (ViaNavigo)
We have made a short list of neighbouring hotels (up to Paris, 40 mins away by train and buses). You can also find affordable local lodging on airbnb or roomlala.