The Viglen was really easy to disassemble by the way. Two screws on the back hold on the backplate, and then the entire motherboard/hard disk assembly slides straight out. Another three screws let you remove the hard drive.
I settled on relatively simple route to install CentOS. I used Red Hat's KVM virtualization to run a VM, attaching the physical hard drive and the (virtual) CentOS DVD ISO. It sounds complicated, but all you need is this virt-install command line to do it (the host is Fedora 10):
virt-install --connect=qemu:///system \
-n centos5 -r 512 \
-v --accelerate \
-c /root/CentOS-5.2-i386-bin-DVD.iso \
-f /dev/sde \
(Adjust the path to the CentOS DVD ISO, and the physical hard drive device as appropriate).
CentOS 5.2 installed in about 15 minutes: