You download the installer from LCPDFR 1.0B and run it. You dont need to complete any mission except the first one if you dont want to keep repeating it over and over when you start the game. Try deleting your save game by going into C:Users**YOUR NAME**AppDataLocalRockstar GamesGTA IVsavegames and delete everything inside and try again. Do NOT save a game with lcpdfr as it will corrupt it. Also make sure you have 1.0.7.0. I think doesnt cut it so if you dont have it, thats why.
Dave