choices[/U] Harry has made to remain good? We've seen Voldemort possess other wizards (Quirrell, for example) and talk of possessing others (Wormtail) and not have a problem. Did Quirrell come to possess any Voldemort powers such as parseltongue?
I'm just trying to figure out where the line is regarding soul-possession verses shared powers. How could such powers be passed on without passing on a vital bit of the original owner? Would it be possible for such a small sliver of Voldemort to reside in Harry that it could rest until it was joined by another, more fully developed piece?
I'm not really arguing for or against Horcrux Harry here-- just puzzling out the logistics...
Of course the cynical answer is that Harry shares whatever power with Voldemort that is convenient for the plot...
And to a certain extent, that's not an entirely invalid answer. I think JKR's world is so well-realized that it is easy to forget that she has to do some things for the book's sake. The prime example - everyone asks "why did Moody have to turn the Triwizard Cup into a Portkey, instead of say, Harry's toothbrush." Well there are a lot of good reasons within the HP world, but another reason is simply that there would be no story if Harry was portkeyed away to the graveyard on page 6.
Anyway, back to the other questions. I guess I see intellect/magical power as essentially the same thing.
We don't really know what kind of Legillimens Harry could be - Snape was only trying to teach him Occlumency, which Harry is far too emotional to do well. I think that the scar itself provided Harry a window into Voldemort's thoughts - one which V. himself had to close after OoTP because V. could no longer tolerate the connection.
But Harry does seem to be acquiring a certain perceptiveness that might be the beginnings of a talent for Legillimency?
For your second question, yes I thoroughly believe that it is Harry's choices that have made him so good. Dumbledore points out that Tom Riddle and Harry had very similar upbringings, but made radically different choices upon entering Hogwarts. Although Harry had every reason to be bitter, vengeful, and miserable, he chose to be hopeful, inquisitive, open.
Quirrell did not seem to be evil, just weak-spirited. Wormtail is a quivering coward and easy to manipulate. Did they have Voldemort's powers when he was possessing them? I don't think so. Quirrell always spoke of V. as "my master" suggesting that Quirrell was still in control of his faculties. At that point V. seemed to be just a voice in Quirrell's head.
I don't think those two were "possessed" in the sense of having their soul crowded out by Voldemort, but that he was controlling their mind - because they were both so ineffectual that they couldn't just follow his orders. Does that make sense?
Now someone who was truly "possessed" by V. was Ginny. While in this state, her own mind/soul/whatever was entirely out of the picture. She didn't remember any of the things Tom Riddle did using her body. She could speak Parseltongue, but it was TR's ability using her voice.
Which makes me wonder why Ginny soul is not too pure for Tom Riddle? I suppose 16 year old Tom Riddle is not quite as evil as Voldemort, so the gulf between Good Ginny and Bad Tom is not as wide. Or perhaps Ginny is pure of heart but weak of will, so she can still be overpowered. Or - going back to the whole choices thing - Ginny is a good person, but her "goodness" has never really been tested. She was born into a happy, loving family, she has always known who she was and where she belonged. She has no reason not to be a good person, no active choice to make to be good.