Install a PCI/PCIe NIC card, and then PXE install from the new NIC.
-or-
Do a CD/DVD installation, and then run the following command to install all (graphics, NIC, audio) drivers:
tools_and_drivers/drivers/linux/OS/install.sh
where tools_and_drivers is the location of the Tools and Drivers DVD, and OS is the directory of the operating system (either red_hat or suse).