OneCare works fine on Vista, so I'm not sure what you are seeking. The Safety Scnner is simply a free online only scanner, not a locally installed version like the subscription product.
However, many of the older CD installs won't work with Vista since they were designed for Windwos XP, so simply go to the OneCare web site and download the trial, then activate it using your same Live ID already used with your other PC.
http://onecare.live.com/standard/en-us/install/install.htmRob