This is what it says on Wikipedia:

Some of the new NPCs include party DJs, a Gypsy Matchmaker and Vampires.

The Sims 2: Nightlife introduces NPC Vampires and allows your Sims to turn into Vampires themselves. By befriending the "Grand Vampires" (also known as the "Count" and "Contessa") who hang out in the downtown area at night, the player can persuade a vampire to bite their Sim. Once a Sim has become a vampire, it receives the characteristic sharp teeth, red eyes and pale skin. Vampires will die if exposed to sunlight for more than a few seconds (they stay within their coffins during the day). A benefit to your Sim being a vampire, however, is that its Needs do not decay during the night. Another advantage vampires possess is the fact that they become immortal, and thus, they will always stay the same age they were when they were first bitten, and never grow any older.

If at any time the Sim grows tired of the vampire life, they can call the Gypsy Matchmaker and receive a potion that changes them back to normal.

Vampires also have no reflection in mirrors, though they will show up in photographs.

How cool is that? Vampires!

I am so going to get it one way or another~ Can't wait!