Watch PCWizKid's detailed walkthrough on enabling this on your Vista PC
You can download a patch / hack from here, After you extract the ZIP file right click on InstallDreamScene.bat and select “Run as Administrator” to install Windows DreamScene on your non-Ultimate version of Vista. Answer “Y” to continue. You can also open elevated command prompt with administrator rights and type InstallDreamScene.bat to execute the batch script. Then Restart your computer.