It depends entirely on the game that you're trying to rip music from. Some require a lot of work while others require little-to-no effort. A lot of companies use formats not supported by anything you can obtain on the internet, this usually leaves you with having to build something that can read those formats. However like I stated previously, it's all dependent on the game and how the developers have it set up.
You could always do a search for game music sites, there's a lot of them out there.