Here's a primer on the PLO from a specialist at the Congressional Research Service. Identifies the major players involved and provides a paragraph or two on each of them.

Summary: During the current Palestinian uprising, several Palestinian factions apparently linked in varying degrees to the Palestine Liberation Organization (PLO) have used violence in an effort to force Israel to end its occupation of Palestinian territory. There is a debate over the degree to which PLO Chairman and Palestinian Authority President Yasir Arafat is willing and able to prevent anti-Israel violence by these factions.