Main Character list -
--Serge, the "new boy" at a French boarding school
--Gilbert, the school slut and Serge's new roommate
--Gilbert's uncle, who is also G's guardian, and who for the life of me I can't remember his name! (I'll watch it again over spring break when I get home)
--the school headmaster (really hot!)
--certain other schoolmates, including the really smart boy who helps Gilbert when he comes home sick/poisoned, Gilbert's two "boyfriends," or rather the two boys who both want to "own" Gilbert, and the really popular boy who befriends Serge and tries to help him "survive" living with Gilbert.

Short synopsis of the story theme -
The basic story of the anime (I haven't read most of the manga, having only volume 10 and being absolutely horrible with kanji) is just that Serge has just arrived as a new student at a French boarding school and is assigned to room with Gilbert, who is the school slut.  (It's a boy's school, btw ^_^)  Gilbert comes stumbling in, having been poisoned by a jealous "boyfriend," and tries to kiss Serge, implying that if Serge helps him, he will sleep with Serge.  Serge pushes him away, gets help, and essentially spends the entire time (of the anime) trying to convince Gilbert that there can be healthy emotional relationships as well as physical ones.  The manga is a bit different, since there are 17 volumes, I think, so the story continues in the manga a bit farther than in the anime.  But the beginnings are fundamentally the same.  There are also a couple of subplots, including one involving Gilbert's uncle (also his guardian), who has a bunch of really weird philosophies on life, such as the belief that mediocrity in people stems from lack of passion and emotions, so he does a lot of really cruel things to Gilbert to make him feel either intense pleasure or intense pain, usually emotional pleasure or pain.  This is one reason that Gilbert is so fucked up.  ^_^;;

What are the potential slash couples and why?

Most obvious: Gilbert x Serge
              Gilbert x one of the two boys who want to own him
Other: Gilbert x uncle
       Gilbert x headmaster
       Serge x the popular boy who befriends him

Links:

Resources:
 http://honeydrop.dreamhost.com/evol/animanga/kaze/
(one of the only known websites on this anime--also has links to other related sites)
http://www.technogirls.org/barbara/anime/tapelist.htm
(where you can get the anime fansubbed in English)