With grub2, you can easily boot a livecd image from your hard drive.
This is general example. It may not work with all livecds.
1. Copy the iso image to root folder for simplicity:
# cp /home/user/downloads/systemrescuecd.iso /src.iso
2. Reboot and when grub2 loads press 'c' for console. Use following commands (tab autocompletion is your friend):
loopback loop (hd0,2)/src.iso