Ethernet and serial are totally different concepts. Hooking a serial console cable to an Ethernet port is rather like hooking an analog phone line to an Ethernet port. They're completely different technologies. They just won't work together. No matter what pinouts/cables/etc you do. It's just different electrically.
You have no choice but to either find a computer with a built-in serial port, or to come up with a expansion card or USB module to add a serial port to your existing computer.
Andy
