To screen shot a virtual machine, make the VirtualBox window active but don't click in the actual VM. Alt-Print Screen should do it then. You'll get the Virtual box window then.

If you click inside the VM and then Print Screen it will copy it to the clipboard inside the VM. VMware has good clipboard sharing, but I'm not sure VirtualBox does.

All Windows 7 disks should be bootable. Your method was round about but glad it worked.