Froyo isn't available for Milestone users at this time. Because the bootloader is still locked, it will only load signed ROMs. This means only ones that carriers or manufacturers release directly. Unfortunately, that means we have to wait until a carrier gives us Froyo. Because the droid has an unlocked bootloader, they can do what they'd like. The difference in root and an unlocked bootloader can be compared to a house. With root, you can paint it any color you'd like but it's still a house. With an unlocked bootloader, you can tear it down and build whatever you'd like in it's place.