Making sure the bios setting has the SATA controller in native mode also tends to help, since combined/emulated ide mode tends to screw up the pata ports under linux when the sata driver loads.
Redhat Enterprise 3 doesn't contain a good guide on how to install and manage a RHEL3 system to a pair of mirrored disks using software RAID. Here's is my guide. This guide should work equally well for the clones of RHEL, e.g. Whitebox linux, CentOS, Tao