I just got back from a datacenter where I installed a new server running CentOS 5.3. I set up a software raid with md0 being /. (Only one mount, didn't split anything up.)
How about /boot? Where's that?
Although I have never done it, you can boot anaconda from grub and I wonder if you couldn't put a ks= as parameter in the grub conf? Setting up software raid in ks is easy. You can also install via url with ks.
Really, you have nothing to lose :)
jlc