How to Boot an Ubuntu ISO from Your Hard Drive

Download the bootable disc image from here.

Install GRUB2 if it is not already installed. Type the following command into the terminal: sudo grub-install --root-directory=/media/grub2 /dev/sda.

Add a menu entry for your Ubuntu ISO. Here are a few examples. Type the following command into the terminal: sudo gedit /etc/grub.d/40_custom and paste these menu entries to the end of the file. Replace /PATH-TO-UBUNTU-ISO/FILENAME.iso with the appropriate path. On my system it would be /home/myUserName/Downloads/lubuntu-natty-i386.iso
=====
menuentry "Ubuntu 10.10 Desktop ISO" {
loopback loop /PATH-TO-UBUNTU-ISO/FILENAME.iso
linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=/PATH-TO-UBUNTU-ISO/FILENAME.iso noeject noprompt splash --
initrd (loop)/casper/initrd.lz
}
menuentry "Linux Mint 10 Gnome ISO" {
loopback loop /FILEPATH/linuxmint10.iso
linux (loop)/casper/vmlinuz
file=/cdrom/preseed/mint.seed boot=casper initrd=/casper/initrd.lz iso-scan/filename=/FILEPATH/linuxmint10.iso noeject noprompt splash --
initrd (loop)/casper/initrd.lz
}