This stategy is for co-op, 2 players.

Get juggernog on the earth/starting place. Now all buy the M14 then kill all the zombies until the sprinter zombies, dogs and nova gas crawlers.

Then you want to do a train around the teleporter pad and the others do a train around the pack a punch. When you both have enough points to pack a punch and buy juggernog, buy juggernog and teleport, but don't pack a punch yet.

Now go and get the space suit, turn on the power and get mule kick. Then get two guns from the box and have pack a punched M1911's, a M14 or an Olympia depending on your taste.

Go to the large dome and do two trains there. When you get to high rounds these trains don't work very well, so when you feel you are going to fail go to the starting place and hack the pack a punch. The gates will close around it and you can fight the zombies freely.

Now when the gates open again, hack the pack a punch again. Keep doing that until it gets too much and then you will die. The end sounds a bit stupid I know, but it's just a bit of fun at the end of the game.