Adding a new drive is usually pretty easy - especially for a Linux desktop with a GUI.
You just install the drive, click a few buttons, and you're done. Piece of cake
* All of this assumes at least a little background knowledge (like the difference between "fat32", "ext4" and "ntfs").
* It's typically the desktop GUI tools that make things "easy".
If all you've got is the command line, then you're going to need the underlying commands.
They aren't necessarily "difficult" - but they *can* be "intimidating"
* Finally, you're DEFINITELY going to need to "know your stuff" if you run into problems.
If this server is as "old" as it sounds ... you're probably going to run into "problems"
I wholeheartedly agree with markush:
Try to find someone who is experienced with Linux and let him/her do this job.
IMHO .. PSM