There are actually three of these hostels called the MIJE. I stayed at the Le Fauconnier, but there are two others very nearby. The phone number puts you through to all three. They are in a great location, in the Marais district, close to the Seine, Notre Dame, Hotel de Ville, and an easy walk to the fantastic Latin Quarter and lots of shops. Most accommodation in Paris is exorbitantly priced, even the hostels, so at around 22 euros a night (including breakfast) in light, spacious dorms in gorgeous old Marais residences, this place isn't bad for value for money. Keep in mind that the accommodation will probably be the most expensive part of your stay in Paris (it was half my daily budget).
If you arrive on the metro, catch it to St Paul and take the tiny street (alleyway) directly behind you; turn left at the end then take the next right.
Also, the maximum stay at the hostels is seven nights and there is a lock-out at 1am.