Windows Updates, Desktop Interaction

Hi All,
Wondering when Windows Update installs updates does it install it in the
"Local System" user context ? If so what happens to the patches if they need
user intervention (like the Win2k3 SP2) ? Does the Windows Update service run
as a "Interact with Desktop" ? or is it just the patch which can interact
with the desktop? What happens if a non-admin user is logged on the "console"
?
Any information ?