This is not a PhysX issue. Many installers from several other software vendors are experiencing the same problem with Vista.
In the mean time you can download the driver to your desktop, and create a shortcut to it by right clicking on the file and selecting "create shortcut". Then right click on the shortcut, then properties. At the end of the target line add the line "/quiet". This will put the installer in silent mode and will ignore any errors the OS is returning. Please ensure that the command line "/quiet" is at the very end of the target line.