I'm pretty sure they are sourced from the same VM's. The only notable difference is that ievms converts (or did when I tried it last) from the VirtualPC copy -

I'm pretty sure they are sourced from the same VM's. The only notable difference is that ievms converts (or did when I tried it last) from the VirtualPC copy - MS is now allowing these for download in other formats (Parallels/VMWare/Virtualbox) without needing to convert.