[quote="bubblegum"]If you don't actually have a second hard disk, then it not set up as a raid. If you don't know what RAID is, then my advice is stay away from it. http://en.wikipedia.org/wiki/RAID
Personally, I would Image (seagate disk utilities is free) the drive you already have, then, install a new larger hard disk in place of the original.
Then restore the image to the new drive.
After that, fit the original drive in the second bay, you can then format this & use it to store documents.
I have installed a second HDD with the Fujitsu kit of parts and used a Fujitsu 160GB second HDD but the computer just hangs when the second drive is attached, so how do I go about solving this issue - Fujitsu technical have been no help at all.