Just to add to HoloCron's comment. Most home users (unless they have specific needs such as RAIDs) will do fine with IDE hard drives. They are very moderately priced and you can get them w/ different speeds and capacity.
SATA (Serial ATA) drives are fairly new on the market. i think they've only been selling them for about a year now. They transfer data at faster rate between your mobo and HDD; of course w/ the faster speed, you will pay a higher price. If you go w/ a SATA drive, make sure you buy a mobo that will support it.