All levels
To get access type SKIPPY on the enter cheats menu.
[Submitted by: Chris]

NOTE: these cheats won't work unless you enable them on the cheats menu.

Codes
Pause the game and select the "Cheats" option on the menu. then enter one of the following codes :

GODLY - God Mode
SORTED - Infinite ammunition
HIDEANDSEEK - Invisibility
SKETCHY - Wire frame mode
SONIC - Run faster
PNTNNP - Second level access
CLAW - Egypt Fodder in multi-player mode
GODDESS - Female Trooper in multi-player mode
UGLY - Hive Fodder in multi-player mode
LEGGY - Hive Guard in multi-player mode
RUBBER - Volcano Guard in multi-player mode
[Submitted by: Sn@ilB8er]

Code
Type in on the cheats menu GOLDENPIE this will give you all weapons, unlimited ammo, invincibility, etc.
[Submitted by: Chris]

All Weapons
Pause the game and select the "Cheats" option on the menu. Select "Enter Cheat", then enter "LOADED" .