The savedgame "All Battlemechs" consist of 12 of all each battlemechs availiable in the game
The savedgame "Ultimate Pilots" consist of pilots with max skills and medals
The savedgame "Ultimate Pilots With All Battlemechs" consist of 12 of all each battlemechs availiable in the game as well as pilots with max skills and medals

To use:
Locate your savegame directory 
e.g. C:\Program Files\Microsoft Games\Mechcommander2\data\savegame\
Unzip both savedgames into the folder
Play the game and click on load the savegame

mr_dott