How to play Area 51 and BeatMania 4th Mix

[Gohan]

I downloaded them from a Bittorrent website and they both come in CHD files
I tried to download Mame082 but i can't get it to work
What should I do?

[raiden]

a .chd is an image of the arcadegame. Some of the newer games require these to be downloaded in order to run the game itself. so the chd file is not a rom, its a hard drive image file needed by the rom. so to run the game you also need to download the rom file for the game.