As jprahman says, you can use another machine to make a bootable USB key with the OS installation files.
But to your original question, you will need a machine to act as the server. This will have DHCP and PXE services as well as the file repository. Server 2008 (and R2) both have this capability built in (seek help on MDT).
But more than likely, if you had the equipment and know-how to do a PXE build, you would also have an external DVD reader and/or a UBS key (to make bootable) to do the installation from as well.