InstallAware

One of our setups is set to require admin rights to install StarOpen.sys into system32\\Drivers.
Some users are now complaining that they still have to switch to an admin account under Vista.
Under witch circumstances is it nessary and which (if any) not?

What might be happening here is that the users that are complaining are trying your installer with the default administrator account. For the installer, the user is an administrator, however in Windows Vista, the default administrator user doesn't have all privileges it used to have in previous versions of Windows. What they need to do is have an administrator user created with full privileges. That will solve the problem.