"Yes, you need to have a copy of Windows to run the VM. Just like a normal PC, it won't boot without an OS. " actually you can boot virtualbox via usb and run a virtual OS without a host OS.
Sorry to bother you again but I downloaded Oracle virtual box and created a VM, but when I try to boot it says: fatal no bootable medium found. I googled it and it means that there is no operating system. Does this mean I have to download windows xp aswell to get the VM to work?