This sounds like the problem I had with Scientific Linux (RHEL clone). The installer did not have drivers for the ethernet chip, but the fully installed distribution did. I was able to perform the installation with a PCI plugin card (my ethernet was on the motherboard), and once the install was done, I was able to install drivers for it. I can't remember whether the drivers came with the distro, or whether I had to download them. In my case, it was a real problem, as my site normally uses network installations. If you are installing from spinning media for the whole installation, you can probably just not install any network, then load the driver/network stuff post-install (assuming you have some alternate means to load the drivers, such as from CD/DVD/FlashDisk.