Game Resource Editor

How many different ways are there to open a resource file? I am trying to create a little editor for a game and can't open the file. If anyone has suggestions or links to a site where I can learn from please reply.

Thanks to all who do.

Are you trying to hack into an exisiting game? Or are you trying to create an editor for a game you're writing?

The game company was in a rush to release the game and never created an editor so we can't edit some images. I wanted to do this for a few people that play the game. They never released any updates for the game, they basically left us. :(

Off-Topic: What game? :p

F-16 Mrf