Here are two links that explain how the voting goes. The first is the normal admittance....through the writers votes. The second is the veterans committee (used for umpires, owners, broadcasters, negro league players, ect)
http://www.baseballhalloffame.org/hofers_and_honorees/rules.htm
http://www.baseballhalloffame.org/hofers_and_honorees/veterans/rules.htm