It is power cable. Seriously, how hard to pull the cable out mate?
The card looks very old too me. Investing a few bucks on a PCI gigabit NIC is not a bad idea (should be ~$10 posted)
You should probably get into hardware a bit more mate (but not too much). It is lot of FUN
Edit: To my best knowledge I dont think it is WoL cable. The entire WoL feature is normally integrated within the NIC chipset. The yellow, red and black wires are typical indicator of a power cable. Also, in many laptops I see similar cable and its purely for power.