UAC is a built-in Vista control which does not allow changes occur within you Program Files Folder, a protective measure to prevent trojan viruses from attacking core applications.  If Poser is installed into Program Files Folder, and UAC is active, any access to your runtime is interfered with.  There are numerous threads addressing this very problem posted here within the forum.  Unfortunately, I don't use Vista, so I can't guide you through the correct steps. 

If you install Poser in it's own separate folder, you bypass the security issues.  The best recommendation populating your runtime is to create external runtimes folders for your content.  This means that those runtimes exist outside the main Poser folder and can be imported into the application.  You can better organize your content and separate them into distinct categories.

The monitor issue, if your mouse stops at the edge of your single existing monitor, all is fine.  I suggest check View in Poser to ascertain if the animation control is checked on.