Unlimited Ammo
Go to the Key Config menu in options. Highlight the AIM function, hold R-HARD, press Z, Z, Z, Z, Z, Z, Z, Z, Z, Z

Unlock Ada Wong
Clear extreme battle mode level 1

Unlock Battle Mode
Clear either scenario with an A rank or better. Don't forget to save the game after the ending

Unlock Chris Redfield
Clear extreme battle mode level 2

Alternate Costumes
To get the special costumes you must do the following. Start a new game on normal difficulty. Don't pick up anything. When you get to the gate that leads to the police station go down the stairs. Down there will be Brad Vickers, the pilot from Resident Evil (he's a ZOMBIE!) Head past him and go up the stairs. Get the herb from the bushes closest to the stairs. Go in the R.P.D. and get the bullets at the desk in the back of the room. Go back to Brad and fill that damb zombie full of bullets. Inspect him and take the special key.
When you get to the dark room there are some lockers, use the key to unlock one and get the costumes. With Claire you get a cool denim jaket and the Colt S.A.A. gun. With Leon you either can choose a leather jacket with a skull on the back or a tank top and a baseball hat

Bonus Weapons
If you finish the game in 2 1/2 hours or less on mission A and get a rank of A or B, you will get the rocket launcher with infinite rounds.
On Mission B you have two options: If you finish the game with an A or B ranking and under 3 hours, you'll get infinite sub-machine gun. If you finish the game with an A or B ranking in under 2 1/2 hours you will get infinite rocket launcher sub-machine gun and the almighty gatling gun

Ranking System
To get an A ranking, beat the game in under three hours and don't use any First Aid sprays. (You can use herbs, though.)
To get a B ranking, just beat the game in under three hours.
To get a C ranking, finish the game in five to seven hours.
For a D rating, finish the game in seven hours or more. Note that your rank will be lowered by one grade if you use any special weapons or if you saved more than 12 times

Unlock Hunk Game
To play as Hunk, beat the A and B games of either character (Leon or Claire) with an A rating on both. Hunk is one of the SWAT members from Umbrella who's mission is to get to the roof-top from the sewers.

Unlock Tofu Game
To play as Tofu you must beat 6 scenarios with an A ranking. Tofu's mission is the same as Hunk's -- get to the rooftop from the sewers. However, it's much harder this time as Tofu is only armed with a knife and cannot use guns