Any help would be appreciated as I am totally stuck!

Only have one account on Vista Home Premium, which I set up when first
loading up the PC - this account is the admin account.

I recently trialled some Adobe software, the software ran out and I
attempted to uninstall.  An error message came up saying I didn't have
sufficient priveledges to write to the key/registry and I couldn't
properly uninstall.  I followed some instructions and tried to make the
key available to access using permissions, this seemed to work.  It
still wasn't working so I searched the net and came across Revo
Uninstaller, and managed to remove all instances of the software.

I then attempted to install some different software and this failed
with a similar message - "do not have permission to access the key"...

Today I tried to load up iTunes and now I'm getting the same message
when double-clicking the logo on desktop.  So I attempted to uninstall
iTunes, then re-install.  I can't uninstall as I get a key error again,
and when I try to install the same error occurs.

Everything points to me not being able to have full permissions to
access the registry, but I can't find out exactly how to:

1. Uninstall correctly
2. Reinstall correctly

If anyone can help I would appreciate it - otherwise, I'm going to wait
until Windows 7 comes out, wipe my HD and do a fresh install

Thanks,
Tony