[Tanniker Smith]

I think any wizard can "go bad", but it's more likely for Slytherins because they're the most ambitious. Slytherin turns out "great" wizards that do "great" things, so long as you remember the definition of "great" as something other than "really, really good".

Look at whatsisname from book 1. THere was no indication that he was a Slytherin, and I believe that he was in charge of either Ravenclaw or Hufflepuff.

TS

[CholeraJoe]

Look at whatsisname from book 1.

Do you mean Professor Quirrel? If so, the book was silent as to his House. He wasn't a Head of House professor, though. Flitwick is Ravenclaw and Sprout is Hufflepuff.

[Politicalmom]

Yeah, but he was actually possessed by old Voldy.