Actually with the newer versions of Linux (like Red Hat 9). You're gonna need some *umph* to your system.. The link that you put up is for the shopping cart and it's a cookie related app, so I can't get to it..
The way a RAID 5 setup works is a little hard to break down.. Basically you have a minimum of 3 drives (for sake of argument lets say they are 40Gb).
In the image above each of the drives has a "stripe" ( A0, B0, C0...) and on one of the drives the "cell" for that "stripe" is what is called a parity cell (Parity 0, Parity 1...) . The way everything work is the parity cell carries the backup information for the rest of the stripe on the other drives. If one of the drives fails, you can reformat and repair just that drive, and then the information on the drive will be rebuilt from the parity information on the other two drives. To explain how that works would go into boolean algebra and binary code information which is to much to work with here. However, suffice to say that it works.... lol..
The total size for the RAID is figured out (using drives of the exact same size) (N-1) * <size of drive> = total size of array. N = the number of drives in the array.
In the case of 3 40GB drives.. you would have (3-1)*40 or an 80GB array. If you were using 6 120GB drives the total size would be (6-1)*120 or a 600GB array. The total size of one drive is used to keep parity (or backup) information on.
What you need to do is to not think of them as separate drives, but all of them as a drive set that work as a team.
If you are seriously thinking about doing this, do some research on RAID Arrays and how they work, because if anything fails, you will need to know how to get it back up and running fast..
Hope this clears some stuff up,