Level skip:
     Pause the game and press Up, Down, Left, Right, Right, Left.

Max ammo:
     Pause the game and press Left, Right, Left, Right, Right, Left.

Refill health:
     Pause the game and press Down, Down, Down, Left, Up, Right.

God mode:
     Pause the game and press Left, Left, Right, Right, Down, Up.

Unlock SegaNet levels:
     At  the  main  menu, select the "Network" option, then choose the
"Account"  selection.  This  should  switch  to  "Account  2". Use the
following configuration:

Login name: admin@sega.net 
Password: tenages (Seganet spelled backwards) 
Area code: Type in your local three digit area code (Ex. 123)
Phone number: Leave blank (do not type in anything) 
Primary DNS or DNS1 = 0.0.0.0 
Secondary DNS or DNS2 = 0.0.0.0 

     Click  on  "Connect"  and  the  game will ask if you want to save
changes.  Click  on "Yes". You should now have access to all levels in
deathmatch  mode  (if  you already have completed the game or used the
"Level  skip"  code).  Go to practice mode to find two new levels that
were  previously locked. Note: Make sure you do this on "Account 2" or
your  online  configuration  will  be overwritten -- and you will then
have to set everything up again.