If you have ever tried to boot a VirtualBox VM into PXE (Microsoft WDS/MDT based) using the default Intel PRO/1000MT Desktop adapter you may have seen the error message

FATAL: Could not read from the boot medium! System halted.

The simple solution to this problem (and to get you booting into WDS) is to install the VirtualBox extension pack which can be found on the same download page as the VirtualBox installer (link).

This extension pack includes the required files for boot to continue normaly, a few screen shots are shown below detailing what you need to do.