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 ...

I'm currently using VMWare Fusion 3.x, not really wanting to upgrade to 4.0, so I've been looking into how to get VirtualBox running with my Boot Camp installation, and so far I'm coming up on ...