A little demo to running Windows XP?

Hi there,

I recently installed VirtualBox on Ubuntu 12.10. I have tried downloading the Windows XP boot .iso to install Windows XP on it. Once doing that, I create a virtual machine, called windowsxp, create a virtual disk, etc. Then, I run it. It says I need to select a boot disk, so I select the .iso. I then click ok, the machine boots, and goes to a screen that says:
"FATAL: No bootable medium found! System halted."

I don't know why this is happening, but I am sure the solution is very easy. I have looked up many other tutorials, but cannot find an answer. Can anyone help?

Thanks,

Barry Smith