Which update of Red Hat Enterprise Linux 3 will run on my HP xw9300? Does it require any special boot parameters?

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.