I'm not 100% sure that the NIC issue is ruled out.
You may be right but, from memory, I think I recall that there is a bit of a difference between a base install (ie what goes on your core) and a MD that is PXE booting. I'm no PXE boot expert but I think what happens is there is a small image that goes across to the MD to get it up and running... now that image can't have all the possible NIC drivers and modules loaded because it's got to be quite small so it may not include the relevant one, even if that one is available to a full 10.04 installation. That's what the whole wiki is supposed to be about - forcing the appropriate module to be in the PXE boot image. Often you don't have to actually download or install drivers... it's just a case of forcing the correct kernel module into the PXE image.
Can you give any more detail of the screen messages when the thing fails?
If it is a NIC issue, you may require the r8168 module... the link http://askubuntu.com/questions/79346/how-can-i-install-the-realtek-rtl8111e-version-8168-driver
implies that this is what is needed instead of the r8169... this is outlined in http://wiki.linuxmce.org/index.php/R8168
But I don't want to send you on a wild goose chase here if the issue isn't an unrecognised NIC.... so those screen messages might help.