By design, if you're logged into Windows Vista as a lesser privileged (non-administrative) user and you try to install software, Windows Vista will stop you. To install software, an LPU must, for a brief moment, switch to an administrative mode.
On the Lenovo X60 tablet I was using, the admin user's id is "David". Unfortunately, when this dialog comes up, it shuts down the entire user interface (see the darkened background) and I couldn't take a screen shot. So, I took a picture of what the User Access Control dialog looked like with my digital camera instead.
One other interesting point.. check out the "action" that this User Account Control dialog is flagging. It says "Internet Explorer Add-on Installer." It doesn't say anything about Adobe's Flash Player. Why is this interesting? Check out what the same dialog says when you're installing the plug-in for Java (next screen)
For David Berlind's write-up on ActiveX control security in Vista and Internet Explorer 7, see his post
in ZDNet's TestBed blog