To get new costumes in the game,start a new game with either character on Normal.
Do not pick anything up.
When you get to the police station you will see some stairs. Go down the stairs and there will be a zombie.
Kill him and he'll drop a ''Special Key''.
Use the key in the lockers in the dark room and there will be a screen that comes up that asks you if you want to switch costumes.
Say yes and you will have the ''new costumes''
Before you use the custom parts on the VP70(Handgun), Desert Eagle(Magnum) or Shotgun use the remaing ammo in the clip/breech. When you use the custom parts to upgrade the gun it will automatically be fully loaded. This may seem like a small amount of ammo but can go a long way in the harder difficuties were ammo is rarer.