I don't use Redhat, by if I remember well, you got a kernel 2.3.x
The Promise controlers are recognized, but not functionning as the kernel didn't keep the addresses (Bug, correct in kernel 2.4.x).
You get two solutions then :
* compile a new 2.4.x kernel enabling external IDE controlers,
* use this
mini-howto . It helped me a lot with Mandrake 7.2