It should be noted first that SATA hard drives are different than IDE hard drives. Furthermore, RAID is simply an alternative way of setting up hard drive configuration, enabling higher speeds and/or data protection. An IDE/RAID combo can be used or a SATA/RAID combo can be used.
It would help if you could post the make/model of your computer so I can look up your bios options and see what you are looking at.. Tampering with these options could cause your computer to not boot...
If you want speed increase, then using the RAID (
level 0 at minimum) configuration would be the setting you need. But in order for that to work you would need a second SATA drive connected to the motherboard. Both drives would be used in
parallel allowing faster data transfers.. Keep in mind that there are many RAID configurations ("levels") that can be used for this, however, the example I gave is just a quick explanation.. If you don't have a second sata drive then you should leave the option in the bios alone..
edit: It should be noted that before deciding to implement RAID on a computer, that some versions of Windows don't support it..
http://support.microsoft.com/kb/314343