Vista usually does this automatically. The only options you have as a user is either to create a new restore point, let the system do it itself during its pre-determined checkpoint, and enable/disable shadow copies/system restore completely.
Sorry for the bum-steer. I'm living in the past, thinking of ME sys res.
You don't have any control in Vista, just this. To store restore points, you need at least 300 megabytes (MB) of free space on each hard disk that has System Protection turned on. System Restore might use up to 15 percent of the space on each disk. As the amount of space fills up with restore points, System Restore will delete older restore points to make room for new ones. System Restore will not run on hard disks smaller than 1 gigabyte (GB).