Are you installing Xp on these drives, or just adding them to your system? If you are installing xp then if I remember correctly you have to disconnect any IDE drives before hand and possibly load sata/raid drivers when the windows setup is loading (pressing F6 when prompted). To create the Raid array in the first place often there is a configuration menu that can be accessed during start up. Look for the button to access it either displayed during boot or in your motherboard documentation.
[size=0.5]CPU: AMD Athlon 64 3000 Socket 754
Mobo: MSI K8T Neo
Memory: Cosair value select 2 X 512MB PC3200 CAS 2.5
HD: 2x 80GB SATA Seagate Barracuda 7200 in Raid 0
Video: Leadtek Geforce 6800 GT
Speakers: Logitech z640 [/size]