When you open UNetbootin, you can select from a menu of Linux distributions the one that you want to try. My 4 GB USB stick was far more than I needed, even for Fedora 17. The current release of ...

Click OK and UNetbootin will prepare your disk. If you’re using the app to download a Linux distro from the internet this could take a while.

If you want to boot into a live Linux environment but don't have a blank CD or thumb drive handy, you can actually boot right from your hard drive using GRUB and previously mentioned Unetbootin.