Um, is that a joke? Cause I know you've been around plenty long enough to have seen a bazillion posts about the Promise RAID controller causing a bazillion headaches.
I think all A7V133's have the RAID 0 option if my review reading has been correct. They may not emphasize it because you can only do RAID 0. The other KT133a raid boards (Iwill KK266-R, the Abit KT7a-raid and maybe others) do RAID 0, 1 and whatever the number is for 4 drives in both raid 0 and 1.
You might check to see that you have the Promise chip installed on your board before you spring for another drive.
I have seen mobos with 0, 1 & 0+1, which takes 4 HD, but not with mode 5 which is like 0+1 buts only requires 3 drives. The controller to do mode 5 is >$400 all by itself on the Promise web site.