The "Bootable" legacy ISO you've used is in fact not bootable, it relies on CDROM emulation provided by BIOS. VMs don't usually do this sort of emulation. If you set the guest OS to something like ...

This is what you should do if your VirtualBox VM boots only in the UEFI Interactive shell. We talk about Windows and Linux ...

I'm a complete nub at this, so excuse my ignorance. I just set up a Windows 7 guest on my OS X 10.6 host through VirtualBox. Took me forever to figure out how to get my flash drive to show up on there ...