Is the 80GB drive the boot drive or a secondary storage drive? If it is the OS drive then you will either have to clone the drive or the better option is to reinstall the OS and all programs. If it is a secondary storage drive you can simply swap them out. However, if the 150GB drive is a new one you will most likely need to format it before using it. Either way you go you should back up all of your important files before doing anything with the drive.