My friend and I heard that there are some hostels in castles around paris. Were not sure if that's right or if it was in paris. So, we would like more info and where to look and how to book etc.

Because nobody replied so far I will ask you one question first. Is it possible you're confusing hostel with hostellerie?

There used to be a "maison des etudiants" in the Marais in a 17th century (approx) mansion near the Palais de Soubise. Unfortuntely that was quite a while ago and I do not remember its full name. Sorry but that is the only thing I can think of.

I have never heard of such a thing. I have heard about one like that in another country, but I can't recall which one, and I do know of one in an old villa or something down in Cap d'Ail.

However, there are none in chateaux in Paris that I know. There is one chain MIJE that has severla hostels in the Marais section in some nice older 17th century buildings, so that would be the closest.
www.mije.com

you might ask on the boards at www.hostels.com or www.eurotrip.com

Haven't found anything about castles in Paris or anywhere in France, that have hostels.....

HOWEVER, if you're traveling to Germany, I found this webpage that lists several castles in Germany that have hostels:

http://www.virtualtourist.com/f/p/9388/

Here's a list of hostels (no castles, sorry) in Paris...

http://www.theglobalexplorer.com/fra...tels/paris.htm

Unusual hostels (i.e. in castles, railway cars, etc) throughout Europe:
http://members.shaw.ca/guideforeurop...lehostels.html

A French castle with a hostel (110 km south of Paris)
http://www.fuaj.org/eng/hostels/aj_f...p?id=47#hostel