AHA! nono, your hard drive cannot also be your cd drive.
Hard Drive picture (out of box)
http://www.tekstation.com/prod_images_large/ACFY2ri4T.jpg
A Hard drive is ALSO called a disc drive or hard disc because it uses solid discs inside to store the data on. Theyre like metallic permanent CD's. Take a look -->
http://www.refurbished-laptops.biz/images/internal-hard-drive.jpg
Nice place to shop for drives -->
http://www.mwave.com/mwave/viewproduct.asp?PID=HD-IDE-WD&updepts=HD-IDE&DNAME=Hard+Drives+-+IDE
CD-Rom or Writer (could also be DVD capable)
http://images.tigerdirect.ca/SKUimages/medium/L12-1044-a1.jpg
You need one of each. a RAID is for more than one hard drive, to protect the data inside. if all you are protecting is your software, games and maybe movies or music, you can always burn them to a CD or regular DVD to protect it. The general home user does not need a RAID array, its more trouble than its worth.
So you will need a Hard Drive, and also, a Disc Drive. The units with built-in DVD-writing and reading capabilities are so cheap nowadays that its silly not to get one. Here is a link to a good all-in-one DVD writer. It will also read and write standard CDs.
Depending on the motherboard you are buying for your system, make sure you match your Hard Drive cable type. There is IDE and SATA. Both use different cable types.
IDE Motherboard sockets -->
http://www.3dnews.ru/documents/3695/ide.jpg
The large black one is usually for your CD Rom. And the Blue one for your Hard drive. The blue one can be used with one cable for BOTH your Hard Drive and CD Rom though, as most manufacturers set their systems up this way. I.E., Dell, Gateway, Compaq, HP, Etc.. etc..
The smaller black one is for a Floppy disc drive. Which are quickly being replaced by USB flash drives, or "memory sticks".
Flash Drive --->
http://www.tomshardware.pl/technews/images/20050921-DT_U3_1GB_HiRES.jpg
IDE Cable. Some come in colors, or round cables, but the connectors are all the same.
http://homepage.igrocom.com.ua/images/cable/ide.jpg
SATA connector on mobo (motherboard) The Black one.
http://www.ixbt.com/storage/serial-ata/sata_conn_big.jpg
SATA cable. they cant get much smaller.
http://www.tekcomputersuk.com/images/sata.jpg
Hope that all made sense! Ask away if you have questions.
I custom-build all the sytems for myself and my company, if you need help on a budget, I can help you out. I also know of a great company always in the top PC magazines that you can build a nice system from, that provides LIFETIME technical support. I have 2 systems from them and theyve never had a problem. One is one year old, the other is over 6 years old.
Let me know if you would like some help, and what your budget is.