Hey Andrew. it gets a bit convoluted when there are multiple problems in the same thread. It would make much more sense if our problems were identical but these are completely different problems. Feel free to start your own thread about this since it will be easier for everyone else to understand. I hope everything works out for you.
I'm running CentOS 4 and this is my /etc/xen config file:
kernel="/boot/vmlinuz-2.6.26-2-xen-686"
ramdisk="/boot/initrd.img-2.6.26-2-xen-686"
memory=512
name="backend"
root="/dev/sda1 ro"
disk=["phy:vg0/backend_root,sda1,w"]
extra="4"
extra="clocksource=jiffies"
extra="console=hvc0 xencons=tty"
vif=["bridge=eth0"]