Instructions
Play your game as your Sim, and visit several community lots to find a pale gray vampire Sim.
Introduce yourself to the vampire Sim and make friends with him.
Build up your relationship with the vampire Sim and wait until he or she bites you (which they will), and you will become a vampire.
Avoid sunlight whenever possible to keep your vampire Sim alive. To do this, make your Sim sleep in his or her coffin during the day, and go out to socialize or explore at night.
Purchase and ingest the Vamprocillin-D potion from the match-maker to revert back to a normal human Sim if you want to.