Sirius, a Slytherin??

[rachelrenee1]

No: HPFGUIDX 32429

I have wondered this over and over, and I think I may have asked this 
as part of a post before.  I always had the impression that Sirius 
and ALL of the Marauders were Gryffindors.  We know that Lily and 
James were Gryffindors and that Sirius was James' best friend.  So 
one would assume that they had to be in the same house, otherwise it 
would really be tough to fine tune a friendship.  It seems quite 
difficult to become friends interhouse, due to the fact you eat, 
sleep, attend class, relax in the common room, etc. with your house.  
(Of course, it seems it can happen, ala Percy and Penelope.  However, 
they were both prefects, so maybe they met at prefect meetings?)

Anyhow, so why do I wonder if Sirius was a Slytherin?  Well, Hagrid 
states in Diagon Alley in PS/SS that there was no witch or wizard 
that went bad that didn't come from Slytherin.  At that time, 
everyone, including Hagrid, thought Sirius was a big time baddie.  So 
was he a Slytherin?  Or perhaps he was the only Gryffindor who went 
bad, and so Hagrid didn't mention it, because the *majority* of evil 
wizards was from Slytherin?

In that vein, what house was Hagrid from?  There was a quiz game on 
the Scholastic site that asked about that and finally (by hitting and 
missing) I discovered that their answer was Hagrid was in 
Hufflepuff.  Where did we learn that in the books?  Has JKR said 
anything?

--Rachel