Hello,
Yes, there is a difference. When UAC is enabled, IE runs in protected mode.
This mode is much, much more restrictive than the mode IE runs in when
running under a standard user account.
When IE is running in protected mode, it cannot save/modify any files on
your computer (other than temporary internet files), save/modify any
registry keys (except for certain ones it needs to work), and it cannot talk
to any other programs on your computer (except for one that is used to ask
you for permission).
In protected mode, when IE wants out of this "protection box", it has to go
through the broker program, which asks you for permission before it
proceeds. In effect, YOU have to know about and approve IE to allow it to
touch any file, registry key, program, etc. on your computer.
In this scenario, if your IE is taken control of by some rogue program, that
rogue program will be unable to damage anything except a few IE settings,
because it will be unable to modify your files/settings/programs (unless it
asks you for permission and you give it the permission).
When protected mode disabled, IE gets the full power of your user account.
So in the same situation with protected mode off, a rogue IE will have as
much access to your computer that you do. If you are running as a standard
user, then it can access all of your documents and settings that affect your
user account. If you are an admin, then the rogue IE can do anything it
wants.