Things You'll Need
Instructions
Travel to the Zombotech Building in San Andreas. With the mod installed, it will appear on your character's radar as a main story mission, making it easy to find.
Enter the Zombotech building.
Speak to either the S.W.A.T. team leader or the man in army fatigues in the main lobby. They have the same dialogue. Either one will give you $2,000 and ask you to kill as many of the zombies as you can. When you exit the building, the mission will have started and every pedestrian in the game will now be a hostile zombie.