Note: This did not work on a Debian Lenny Host. It worked OK for Debian Squeeze (with more recent libvirt and kvm).

virsh shutdown deb01 //make sure it actually shuts down via acpi virsh edit deb01 //add in the bold lines below

 <os>
  <type arch='i686' machine='pc'>hvm</type>
  <boot dev='hd'/>
  **<boot dev='cdrom'/>**         <nowiki>//</nowiki>add this line
  **<bootmenu enable='yes'/>**    <nowiki>//</nowiki>add this line
</os>

…..

   <disk type='file' device='cdrom'>
    <target dev='hdc' bus='ide'/>
    **<source file='/root/gparted-live-0.7.1-1.iso'/>**    <nowiki>//</nowiki>add this line
    <readonly/>
  </disk>

virsh start deb01

The manual approach to get KVM to boot off a cdrom is only to have the line: <boot dev='cdrom'/>

Once you start the VM (virsh start vm), connect using VNC. You can right-click on the VNC window titlebar, send a CTRL+ALT+DELETE to reboot the VM and then press F12 to see the boot bios.

http://wiki.kartbuilding.net/images/kvm-bios-boot-menu.jpg