well there is only 1 tip i can give you...
when you get to a tricky part of the game, deliberately die then choose to save. if it takes you a lot of credits to do the bit your on, turn the neo off and load up your game, youll then have all the credits left. this trick is particualrly handy when you get to the minecart section at the end of the game. oh and the secret guy is called 'tequila' he's the trator you capture on mission 16? i think that's the one. why the other army guys would attack him though, i dunno! they all look the same!