Files on D: from XP have strange user under Security.

Hey.
When going from XP Home to Vista Ultimate i had all my files that I needed
on D:.
Now I have some problems with files on D:
The porblem I get is that files that I had there form XP, I cant move
without Admin status (have to click on Continue in a window) and other
things like that.
New files that I download I can do whatever I want to (as I am the owner of
them).

I guessed it had something to do with user rights.
So I looked at some files security tab and there is a User with a "?" on the
user icon and with a name starting with "S-1-5-21-..." and like 20 more
numbers and some files and folders have other groups there then others (some
of them have "Creator Owner" and some have others).
None of the files or folders have the "Certified Users" group (or what ever
it is cald in English Vista) that the folders on C: have.
So I guess this was there from XP?
Anyway so I went to the Security tap for D: and set my user name to owner of
all the files on D:.
So now in security on all the file my name is where the S-1-5-21-..." user
was.
But on some of the folders and files that user is still there and my user
did not get added as owner.
So for some reason some folders did not get the settings I changed for D:.

What I'm trying to say is that the security settings on all the files on D:
are a mess.

I'm guessing this is the same problem others are having that complain about
having to always click on bottons just to move a file and not being able to
edit and save text files with notepad.
I got this to not happen by setting my user as owner.
But as I said, some files and folders did not change.

What I want to know is if there is a way to reset/remove all the Security
settings on all the files and foulders on D: so they dont have security
settings from XP on them anymore and get the settings (Users and Groups)
that Vista wants them to have.

I'm glad my 300 GB External HDD dont have security settings on any files.
I just found out that moving files to my External HDD and back removes the
security settings and makes new ones so I'm thinking about just moveing
everything on D: over to the External HDD and then back (just have to make
some room first.

Sorry if this is not typed wary good.
Its late and I am realy tierd.
And my Eenglish is maybe not the best in the world

Any help is more then welcome.
Thanks.
And I hope this might help someone else having problems with this.