Q: How can I PXE boot my Surface Pro over the network?
A. At time of writing it's not possible to PXE boot the Surface Pro over the network, as this capability isn't enabled in the firmware. It's expected there will be a firmware update that should add PXE boot support when used with the Microsoft USB Ethernet adapter for the Surface Pro.
This PXE boot won't extend to third-party USB Ethernet adapters (although they can be used for general Ethernet connectivity). Support of third-party Ethernet adapters might be added in the future but requires support in the firmware for the other types of USB Ethernet adapters.