When your weapon is almost out of ammo, conceal it and bring it back to your hand immediately - it will be fully loaded. Works on many weapons.

When playing The Meat King's Party look at the loading screen of the slaughter house. You should see a faint skull. This skull is also on the pinball machines in Rotterdam Rendezvous.

To get the silent assasin rating and a bonus weapon you have to meet certain requirements.

They are as follows:

Accomplish all mission objectives only killing the target unless the objectives say otherwise, you have to kill the target with an enviormental hazard (i.e. rat poison), one silenced bullet or your fiber wire. You also cannot be seen more than three times.

You unlock these weapons after acheiving the Silent Assassin Rating on the corresponding mission

Mission 1 CZ 2000 dual pistols
Mission 2 Micro uzi dual submachine guns
Mission 3 Silverballer silenced dual pistols
Mission 4 Magnum 500 dual pistols
Mission 5 Sawed-off shotgun dual
Mission 6 M4 Carbine Silenced assault rifle
Mission 7 SG220 .S dual pistols
Mission 8 MP5 silenced submachine gun
Mission 9 AK 74 Silenced assault rifle
Mission 10 GK 17 dual pistols
Mission 11 Micro uzi silenced dual submachine guns
Mission 12 PGM Silenced sniper rifle

On Asylum Aftermath, if you go up to the third floor and out onto the balcony of the front of the Asylum, you'll find a patient balanced on the edge of the balcony. When he sees you approach, he'll say something in a foreign language to you and throw himself to his doom.

Find the "hitmancontracts.ini" file in your C:\Program Files\Eidos\Hitman Contracts directory. Add the following two lines to the end of it and save changes:

ENABLECONSOLE 1
EnableCheats 1

Now when you press Shift+Esc ingame, you can access a cheats menu which will allow you a range of things like God Mode, infinite ammunition, control over the speed of time, the ability to teleport and more!