For instructions on how to configure the network interface card with PXE support to boot from the network, consult the documentation for the NIC. It varies slightly per card.
If your NIC does not support PXE booting, you can still PXE boot your system by using the
gPXE bootloader. Red Hat does not distribute
gPXE — refer to the Etherboot Project website at
http://etherboot.org/wiki/start for more information.