You should be able to override the old path depending how old the installers are.  Some DAZ files will actively search your hard drive for Poser.exe file and allow you the option to install in multiple Poser programs.  You could actually cancel this and install it manually.  Other individualy like to uninstall in a temporary folder and then manually transfer the content to either the primary Poser runtime or external runtimes.  Now I don't believe that you can redirect your installations using any local settings in Vista (Sorry, not very familiar with the OS yet).  I believe the installs are hard wired in the files themselves.