The sorting hat seems to think Harry is a pure-blooded wizard.

[iamvine]

No: HPFGUIDX 105766

--- In HPforGrownups at yahoogroups.com, "Cathy Drolet" <cldrolet at s...>
wrote:
> Jenni said:
> 
> "For instance, Slytherin
> Took only pure-blood wizards
> Of great cunning, just like him,"
> ------
> 
> Cathy:
> 
> I think the operative word there is 'took'.  When Slytherin was in
charge he may well have sorted out the pure-blood kids and took them
to teach.  I don't, for a second, believe the sorting hat is still
operating this way or it would not have sorted Tom Riddle into
Slytherin or tried to sort Harry there.  I think there is a lot more
than meets the eye to that old hat (which was, after all Goderic
Gryffindor's) and I think we may yet find out a couple of the
Slytherin kids are not pure-bloods either which may create a bit of
trouble in books 6 & 7.

Eleanor:

Which makes Salazar Slytherin just one of a long line of thinkers down
through history whose ideas have been twisted by subsequent generations.

I wonder if it's possible for a Muggle-born to be put in Slytherin
after all.  Some of the Muggle aristocracy, after all, have or had
similar ideas about themselves to pure-blood wizards.  A magical child
born to that background wouldn't yet be aware of their own status in
the wizarding world when they first arrived at Hogwarts.  If their
personality was suitable, the Hat might put them in Slytherin and
they'd then get a nasty shock when they found out how other Slytherins
viewed them.

The HBP might be a candidate for this treatment (if he's a prince in
Muggle terms - my imagination is coming up with ideas about a royal
Muggle who turns out to have married a witch, and whose child is
vulnerable to being used by Voldemort to gain influence in Muggle
society).

Eleanor