Play as Vicki
You may have to wait till 3DO releases Portal Runner to see Vicki in her own game -- but for now, you can at least play as her in Sarge's Heroes 2. Simply select the Enter Code option on the main menu, then enter the "Green Girl Rocks" code:
GRNGRLRX

Maximum Ammunition
Select the Enter Code option from the main menu, then enter the following code to have maximum ammunition:
SLGFST

Tin Men
Select the Enter Code option from the main menu, then enter the following code to play as Tin Man:
TNMN

Level Passwords
Want to unlock all the levels in Sarge's Heroes 2? Enter the following codes at the Codes Menu (accessible from the Main Menu):
Level 2 (Bridge): FLLNGDWN
Level 3 (Fridge): GTMLK
Level 4 (Freezer): CHLLBB
Level 5 (Inside Wall): CLSNGN
Level 6 (Graveyard): DGTHS
Level 7 (Castle): RNKNSTN
Level 8 (Tan Base): BDBZ
Level 9 (Revenge): LBBCK
Level 10 (Desk): DSKJB
Level 11 (Bed): GTSLP
Level 12 (Blue Town): SMLLVLL
Level 13 (Cashier): CHRGT
Level 14 (Train): NTBRT
Level 15 (Rockets): RDGLR
Level 16 (Pool Table): FSTNLS
Level 17 (Pinball): WHSWZRD

Tiny Soldier
Select the Enter Code option from the main menu, then enter the following code to play as a tiny soldier:
DRVLLVSMM

Play as Plastro
Select the Enter Code option from the main menu, then enter the following code to play as Plastro:
PLSTRLVSVG

All Weapons
Select the Enter Code option from the main menu, then enter the following code to have all weapons:
GBZRK

Display Debug Information
Select the Enter Code option from the main menu, then enter the following code to display the debug information:
THDTST