This cheat involves creating a .txt file in the game directory. Name the file LOCAL.INI and add these cheats to the text.

All cars in all episodes: FE_UNLOCK_ALL_CARS=TRUE
Skip to the next mission: CanAlwaysPlayNext=TRUE
Car becomes monster truck: MONSTER_TRUCK=TRUE
Car get big bands: CARLOS_FANDANGO=TRUE
Auto-Play: PlayerUseAI=TRUE CPU
Disables conversations: PlayConversations=FALSE
Disables sound: DisableAllSound=TRUE
Disables skid marks: DisableSkidMarks=TRUE
Enables free roam mode: FE_Enable_Free_Roam=TRUE