You need to go to a community lot and wait until a witch arrives. Then, befriend the witch and when you have done so, there should be an interaction saying "Teach me the ways of the ...". -A
Chat with our AI personalities
You can not make a Sim anorexic.
You can't make a Sim beg for money.
No, elder Sims can not get pregnant.
My guess is that you can't make your sim to a vampire on the sims 3.
Well there is no cheat all you have to do is make your Sims do their homework. If you have Sims 2 Seasons you have your sim drink apple juice before they do their homework. It will help them do it faster.