I just bought the "Vue 5/Poser 6/Mover 5" bundle so I didn’t have any previous installation, but I did notice that on the Application CD there is a folder called "Add-onsMover" and in there was an installer called Mover5ForVue5Installer.exe. The About.txt says:

---- About.txt ----
The Mover5ForVue5Installer application is designed to let you use your Mover license within Vue 5.

If you purchased Mover 4 or Mover 5 for Vue 4, you do not need to purchase a new copy in order to use it with Vue 5. Instead, simply run the Mover5ForVue5Installer application in this folder. This will install Mover into your copy of Vue 5 (you will be prompted for your Mover serial number).

So it looks like you need to run this installer and supply your Mover 4 serial number to unlock it. Hope this helps.

~jr