Personally, I would 
1. Back up critical files.
2. Power down the server and add the second drive (on the second IDE
channel if possible).
3. Bring the box back up.
4. Log in as root
5. fdisk the new drive
6. add the the filesystem of your choice
7. mount the new partition
8. copy the /home directory over to it
9. edit your fstab to point /home to the new partition on the new drive
10. reboot
11. log in as root to the maintenance console and fix any typos you may
have made to the fstab file. 
12. reboot again and enjoy your new drive  
Provided everything went well you should have just moved your /home
directory to the bigger drive and left everything else alone.  A bonus
in this situation is that you also have a backup of your /home directory
that you can move back to with an fstab change if something goes south
in the process of adding the new drive.