I think you may have to backup your files first, moving the os over requires something like Acronis True Image unless you wish to just reinstall it via the install disk or usb key. As long as you don't change motherboards the OS can normally be reinstalled since its tied to that mobo.
You'll want to look into raid to make the two 2 TB hdds a single volume. Keep in mind theirs different versions of raid to look into, all for different users/uses. You most likely want to see about JBOD or RAID 0