[dnanian]

Right. You'll basically do a full backup to the external LaCie (name it the same as the internal drive), using "Backup - all files". Boot from the LaCie to make sure it's OK. Then, shut down and replace the drive.

Boot back from the LaCie and prepare the internal drive, once again using the same volume name. Then, use "Backup - all files" to copy back from the LaCie to the internal.

Shut down, detach the LaCie, and boot up from the internal. Make sure it's all OK, and you're set!