In The Sims 2 University, when attempting to join a Greek house, Sims from that household will then come over to your home lot and the game will initiate what some call the rush mini-game. In order to be accepted, you will need to build your relationship with all the members within five hours, otherwise you will be rejected.
Household Rush is a brand new mod in the making that brings this functionality into The Sims 3. It's designed mainly for university, but works for joining households in the home world too. It can be used to join a fraternity/sorority houses as well as normal households.
The mod does basically the same thing that's included as a feature in The Sims 2. When you successfully complete the challenge, you will be moved into the household's lot and all the household members will become roommates.
Due to limitations of the system, the entire playable household will be moved, though only one Sim has to complete the challenge.