Running VirtualBox VM host on ReadyNAS Pro

Hi guys. Sorry, me again, with issues, again.

I (think I) have installed VB successfully, but am having trouble installing Ubuntu Lucid on it. I have a ReadyNAS Ultra 4 (RAIDiator 4.2.17), and have installed the latest RNDP6xxx_4.2.17_WW_src.zip GPL, and installed VB using VirtualBox-4.0.8-71778-Linux_amd64.run following the instructions here: viewtopic.php?f=35&t=26468&p=296922#p296922

So that got VB onto my system. Can't find the reference URL now for how I followed instructions, but this is how I set up VB ready to install Lucid:

# VBoxManage setproperty machinefolder "`pwd`"
# VBoxManage createvm --name "Lucid" --ostype Ubuntu --register
# VBoxManage modifyvm "Lucid" --memory 1024 --acpi on --boot1 dvd --boot2 disk --boot3 none --nic1 nat
# VBoxManage modifyvm "Lucid" --pae off --nestedpaging off --vtxvpid off --hwvirtex off --hwvirtexexcl off --ioapic off
# VBoxManage modifyvm "Lucid" --vram 32 --usb off --usbehci off
# VBoxManage createhd --filename "Lucid.vdi" --size 10000
# VBoxManage storagectl "Lucid" --name "IDE Controller" --add ide --controller PIIX4
# VBoxManage storageattach "Lucid" --storagectl "IDE Controller" --port 0 --device 0 --type hdd --medium "Lucid.vdi"
# VBoxManage storageattach "Lucid" --storagectl "IDE Controller" --port 0 --device 1 --type dvddrive --medium "../downloads/ubuntu-10.04.2-server-i386.iso"
# VBoxHeadless -startvm "Lucid"

After that last command, the VB "boots up" and starts going through the Ubuntu install process. Everything looks ok (viewing progress through RDP viewer), and gets up to the stage where packages are being installed. That gets to about 83% where it's trying to installed the kernel image, then it just hangs for ages, then the VB headless process exits or times out after a while.

Any ideas from here? I must be close, but something to do with the new kernel?... Hang on... Should that Ubuntu version I'm installing be "i386" or "AMD64"? Could that be it?