Hard Disk failing, need to repair

I bought a 13" MacBook Pro 1 1/2 years ago. It had Snow Lepoard installed. Since then I upgraded to Lion, through the App store. My hard disk is now failing and I need to get it up long enough to do a backup. I tried to reinstall the OS, but get errors throught eh app store, and when I put the snow leopard disk in, it cannot install it on my hard drive, as it is a newer version, How can I get lion on a CD to boot from?