Not able to install linux




I'm trying to install linux on my pc. Configuration is :

Motherboard : Asus m5a97 evo.

HDD : 2 TB & 80 GB ( Installing linux on 80GB)

Ram : 16GB

Graphics card : ATI 7850.

I'm trying to install RHEL 4.

But during installing i get a msg about some drivers missing. After some research found out the problem is with AHCI controller. For the very same reason i was not able to install Win XP. So changed the sata controller to IDE. I was able to install XP but not linux.

Please help..... :(

There is option in BIOS setting to change HDD mode to AHCI,