These cheats, hints and unlockables work with the PSX (PS1), Dreamcast and PC versions of Dino Crisis.

Unlock bonus outfits for Regina
Complete the game for the first time and you will unlock two new costumes (Battle type, and Army type. The third costume will unlock after completing the game a second time. The fourth and final outift can be unlocked after completing the game in under 8 hours. All bonus outfits will carry over into your next game.

Grenade Launcher with Infinite Ammo
When you have seen all 3 endings to Dino Crisis (more info below), Regina will begin her fourth game with an infinite ammo grenade launcher in her inventory.

How to Trigger the Different Endings
Ending 1: When given the option, choose to go with Rick.
Ending 2: When given the option, choose to go with Gail.
Ending 3: "If you've played through to the end and chosen both Rick's and Gail's choices, then here's the final ending you're looking for. Have a feeling you've been through the game without visiting a few doors? You have. Three, to be exact. If you want to find it, you can simply access one of the Level A doors after you've chosen Rick or Gail's decision. All of the unexplored level A doors lead to the same tunnel system. Simply follow it the secret heliport, then check your map and visit the red room." [Source]

Unlock Operation Wipeout Mode
To unlock Operation Wipeout mode, complete the game in under 5 hours, or save less than a total of 3 times, or don't use any continues.