You can only the setting in your BIOS if you have a SATA drive and a motherboard that has a SATA controller. You also can only use AHCI if your OS has the drivers installed. Windows XP does not have native SATA drivers, they can be can be intalled after the installation of the OS, but must be installed before the BIOS change. Windows Vista and Windows 7 have native SATA drivers, but again they have to be installed before the BIOS change. The following link describes haow to install the SATA drivers for Windows XP on a motherboard with a Intel chipset: http://saysprasad.wordpress.com/2009/02/01/installing-sata-drivers-for-enabling-sata-native-mode-after-installing-windows-xp/