StartupDisk

You can make an installer on a USB memory ( >= 2GB).

At first, reboot from a installation DVD.

Click the "Try Ubuntu" button, and wait.

Insert a USB memory to your PC.

Search for the "usb", and launch the "Startup Disk Creator".

Click the "Other..." button to search for an ISO image file.

Click the "Make Startup Disk" button.

Click the "Yes" button.

wait the following dialog box.

Click "Quit" button.

Now, you can use the USB memory as a installer media.