How to turn off RAID,AHCI confuguration on dell S490. Am unable to install Windows XPSP2 with only SATA HDD?

Message=Press F6 if need to install scsi,raid drivers. No boot device found. Dell says 1st. set bios to raid on save & exit. I have. They say nextgo into I menu & choose disks non-raid.How do I get to this I-menu. what I really want is a way to keep raid & ahci on. because the speed of the sys.suffers without AHCI capabilities. Ultimately I need to download the drivers,but am having trouble with this also.