It would help if you gave the brand/model of your HDD. I can say, though, that XP dosen't do very well "out of the box" with SATA drives. I'd check the website of your drive's manufacturer and see if they've got some kind of utility you can download.
Go ahead and convert and format it- see what happens.
make sure you don't have any info on those drives you can't lose first.
I would double check your bios to make sure the drives are showing there correctly first.
Then- you might want to hit the MFG site and install the RAID drivers and such.
I am sure windows does not reckonize the drives, or the array becuase it lacks the drivers. Run the install CD, or download the driver package and windows should detect your new hardware and allow you to format, partition and make active the drives.