>set root=(hd0,2)
>loopback loop (hd0,2)/ubuntu-11.04-desktop-i386.iso
>linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=/ubuntu-11.04-desktop-i386.iso
>initrd (loop)/casper/initrd.lz
>boot
上邊的參數根據實際情況修改
http://forum.ubuntu.org.cn/viewtopic.php?f=86&t=6511&start=0
請參考該鏈接