OK, the kernel will misread your card as a standard ide controller.
You'll have to insert the driver into the running kernel during install by installing in expert mode
First get
http://www.promise.com/support/file/T-FTS-02-RHD73.zip
NOTE: these drivers state they are for RH7.1/7.2/7.3... I haven't tested them on RH8
Unpack both zip files from this archive and unpack either rhup.zip (uniprocessor) or rhsmp.zip (SMP) onto a floppy.
Start your installation, at the boot: prompt type expert
Go through the install as per normal, it will prompt you to insert third party drivers, when this happens whack in your disk.
You should be able to setup your partitions etc and continue with your install.
When the installation is complete DO NOT REBOOT.
You have to shell out [ ctrl-alt-f2 ], insert your floppy in the drive again and issue the commands
# chroot /mnt/sysimage
# mount /dev/fd0 /mnt
# cd /mnt
# sh setup-ft
# cd /
# umount /mnt
# exit
This sets your root to /mnt/sysimage and installs the ft.o driver (amongst other things) so it loads during boot.
Checkout the README in the packages...