I'm assuming you mean a blown on-board NIC. In which case, if the board still boots and runs, and just the NIC doesn't work, i'd run a PCI add-in NIC (preferably) or a USB NIC if you have no available PCI slots. I personally don't care for USB NICs but they can get you out of a bind. I'm not sure how cost effective doing board-level repair is going to be though, since these are really old boards, and a modern, cheap, single processor board and chip is going to run circles around a pair of old-school 533FSB skt 604 xeons.