"Administrator" Madness: How Do I Convince Vista?

I'm about to install RC1, but before I do I need to know what went wrong
between 5384 and 5742. I installed 5384 and, buggy as it was, I never had
administrator/access problems. Fast forward 10 weeks, I fresh install 5742,
and suddenly I can't download a %^@! mp3 file from a pay service without
getting a 'You do not have the right to save a fiel to that folder. Save to
a temp folder instead?' type-error -- which, most often, would then tell me I
couldn't save to the temp folder either.

I understand security is a big issue in Vista, and I've been patiently
dealing with User Access Management since June. But I have only one profile
on this machine; so how can it not know I am the admin? Why would it deny me
access to saving downloaded files in my own User > Documents folder? I have
never tried to log/boot/access as anything else.

I'm pretty savvy with this (not a tech, but a 'high end user'), and it
baffles me how normals will muddle through the new access restrictions.

T.M.