Yes the Gateway should be set to 192.168.168.1 and PC set to 192.168.168.100

You will lose the connections to rest of your network and the internet (because the router is set to .1.xxx vs .168.xxx) but for configuration that should not matter -- all you want is the connection to the miner so you can change it to use DHCP. Have you tried just directly connected the miner to the PC? Assuming the LAN cable is a crossover type (most are) it should work. It not sure about the cable, just connect the 2 through a switch and it will figure out which are the Tx and Rx lines. Once you do get connected, only change the miner to use DHCP, save then reboot it. Change the PC addresss back to your original and you should now see the miner on the router. Once you see it there, get it's address, log in to miner and then put in the user and pool info.