RHEL4 has very limited support for SATA interfaces which is why the hard drives is not known. You may need to set the SATA interface to legacy mode in the BIOS and try at the installation menu screen;
linux text all-generic-ide
You could wait a couple of weeks for RHEL5 or try SL5 Alpha now, both have much improved SATA support. SL5 Alpha is a pre-release 100% binary compatible freely 'clone' of RHEL5beta2 with some updates.
https://www.scientificlinux.org/news/sl5.alpha.live