Some NICs have an option to boot to a network server, i have never seen it done, but I know that there used to be something you could install on a win95 machine to make a clone image that would be available for network boot with machines with NIC's that support booting. It would remotely mount the image as a C: drive locally and boot off it. Way back in high school we used to have a ton of 386s with the really old Ethernet and none of them had hard drives, they all booted up DOS from the network server (486) running some sort of novel server.
If you figure out how it works anymore, I would be interested as this makes for an easy thin client.
foxkm