Installed XP when BIOS had SATA set to IDE mode, can I change to RAID?

I am contemplating giving a RAID array a try to see if it will increase my performance with games and large file transfers but when I installed XP I had to install it in IDE mode. I found a place where a guy had a tweak to change it from IDE to ACHI mode (otherwise it is not bootable) but I was wondering if this were possible for Windows XP. Would it make any difference if my XP install wasn't striped in performance or would it only show an improvement on games and other applications I installed after setting up the RAID (RAID 0 I guess)? I have seen in a couple other places that in real-world benchmarks the performance improvement for RAID 0 isn't that much (game performance was one example).

Here is something from Wikipedia that I don't quite understand: "For reads and writes that are larger than the stripe size, such as copying files or video playback, the disks will be seeking to the same position on each disk, so the seek time of the array will be the same as that of a single drive." So I am assuming that means that operations on large files do not really see much of an improvement with a RAID 0 setup. Are there any other issues like copying really small files with RAID?

Also, you can have partitions on a RAID array right, except the partition spans both drives? Could you also reliably back up a RAID partition using a cloning program if you have the RAID drivers loaded? Thanks.