I suspect that the problem is that the motherboard is so new that it's not supported in the 2.6.26 version of the kernel: when I looked at the Intel webpage relevant to the board,
http://www.intel.com/support/motherboards/desktop/dh55tc/sb/CS-031186.htm, it suggests that a LAN driver may be needed for Linux, and I infer from their table of information that this is more likely to be the case for kernel versions prior to about 2.6.31.