From the sound of it, your older drive is using an older SATA, probably SATA 2 3gb/s. You can use this as your primary drive if you like, however, it will not have the speed and performance of your new drive. If I were you, I would use Samsung's data migration software to transfer the OS and files from your old drive to your new drive. If you do not want to use Samsung's data migration software you will need to do a fresh install of windows 8 on your new drive, just make sure to backup your files first. I would avoid imaging your old HDD as this may give you some problems in the future.
As for putting your drive into raid 0; once you set up your new drive, I would trash the old drive.
You might find these links helpful.
Samsung Data Migration: http://www.samsung.com/global/business/semiconductor/samsungssd/downloads.html