PXE/IPXE/GPXE are all network boot methods. I personally have never heard of a way to network boot a virtual hard drive.
Microsoft has their own way of using images and ways to distribute them. Generally it is a server configuration where an image can be sent to then load to a hard drive.
Maybe I don't get your question.
Some people can make BartsPE or UBCD4win that will boot via pxe.
http://reboot.pro/topic/19015-boot-m...work-via-ipxe/