First, back up everything, because it will be lost when you create the array.
Then, get out your CD that came with your mobo and make a floppy with the RAID drivers. There should be a "make disk" utility in the folder with the RAID drivers for your mobo.
Go into your BIOS and enable the RAID and make it the boot drive. (consult your mobo manual)
Hook your drives up to the right connector(s) (consult your mobo manual)
boot up and enter the RAID BIOS (consult your mobo manual)
it's pretty easy to figure out how to create an array, you do it in the RAID BIOS (consult your mobo manual)
Once the array is created, exit the RAID BIOS and insert your XP CD.
Right as the CD starts the setup you will see "Press F6 to install SCSI or RAID drivers." Hit F6
It will then take a minute, and come to a screen asking you to hit "S" to install a SCSI or RIAD device. Hit S
It will then ask you to insert the floppy with the drivers. Pop it in, and hit "enter."
When that is done, it will ask you to hit S again if you have more drivers, or enter to continue. Hit enter.
Leave the floppy in, it will need it in a few minutes. After it needs it the second time, take it out before Windows reboots or you may have trouble.
You're done.