I've installed RH9.0 on a machine using a Promise ATA RAID card with no probs.
It's a weird error you are getting, have you tried disabling your serial ports in the BIOS? Just to test if it is that, cuz that's what the TTYSx is.
If you do have the IDE RAID setup, you'll need to install the drivers during your linux install. I downloaded the latest ones from www.promise.com
To install the drivers at install time, when you boot of RH CD1, type in linux dd at the first prompt you get after booting off the cd.
You'll need to extract the drivers onto a floppy and stick it in your machine.