In order to receive support from Red Hat on the HP xw9300 on the 32 or 64 bit version you will have to install Red Hat Enterprise Linux 3 Update 5 and have BIOS 1.21 or later.

Additionally, when running the 64 bit version of Red Hat Enterprise Linux 3 you should add the numa=off option to the kernel line in your /etc/grub.conf file to prevent premature swapping.

default=0
timeout=10
splashimage=(hd0,0)/grub/splash.xpm.gz
title Red Hat Enterprise Linux AS (2.4.21-32.ELsmp)
        root (hd0,0)
        kernel /vmlinuz-2.4.21-32.ELsmp ro root=LABEL=/ numa=off
        initrd /initrd-2.4.21-32.ELsmp.img

Booting with acpi=off will cause a kernel panic. This option is not currently supported for the xw9300 on Red Hat Enterprise Linux 3.