Could someone walk me through building a 3 machine postgres cluster with automatic fail over? I've searched and searched and I'm just not getting it.

I currently have postgres 9.1 installed with 1 database as 9.1/main. I'd like to cluster this to provide ha and faster query times. Writes to the DB can be forced to the master only, so read-only slaves are okay (there are far more reads than writes)

Can anyone help me out?