I wanted to document this somewhere before going over to the server room…
To get Debian to install on a Dell 1950 you need to use the Debian Installer for Testing (Etch). Also, before installing grub (at the end of the installation), you need to perform the following tasks:
echo "megaraid_sas" >> /etc/mkinitramfs/modules
mkinitramfs -o /boot/initrd.img-2.6.15-1-486 2.6.15-1-486
This will include the megaraid_sas module in your initrd.img, (allowing the kernel to find your PERC/5 RAID array).