Installing the community bonus pack for Unreal Tournament 3

On PC custom content goes in your Documents folder, not the game install: My Games\Unreal Tournament 3\UTGame\Published\CookedPC. If Published and CookedPC aren't there, just make them. Extract the pack so its folders sit straight inside CookedPC. The usual mistake is unzipping into a new folder and ending up one level too deep, then nothing shows in the map list. If the maps don't appear, look for that extra folder first.