Vista - NTFS file permission

Hello fellow vis(t)ionaries,

I have 3 questions:
Recently I installed Windows Vista, like most of us. I didn't had the
upgrade option, so I did a full install.
After installing I realized I had a folder/files on an external Disk Drive,
with NTFS file Permission. Result is I cannot acces the folder/files anymore.
I tried to take ownership, which I'm not permitted to. I can retrieve the
files, after some intense work, so I prefer keeping them, but I wouldn't care
a lot losing them, so I tried to delete them. I don't have sufficient
permissions for this, neither. The files are occupying a 28 GB (more or less,
windows says the folder's empty which it's not), so that's kind of space I'd
like to recover.
I still remeber login and password, so, is there anyway I can recover/delete
these files, without formatting). (1)
I know there's a difference between User (administrator) and Administrator,
I don't know how to log-on as the latter (how? 2), and does it make a
difference to my kind of problem? (3)

thank in advance,
Christophe