When you say network drop is fine does that mean from the switch to your computer? Have you tried a different port on your switch?
I've used my laptop on the same network drop... I've changed from port A to B in this cube and I've tried A and B in the cube next to me... all four ports produce the same result with the system but work fine with my laptop.
What if you boot with a CentOS 5 LiveCD, CentOS 4 LiveCD, or Knoppix on your system?
Barry