How Do I download a Sega dreamcast emulator?

Ive been looking up how to download the dreamcast emulator for 4 days now and still don't get it I love the dream cast and all its games I use to play as a kid so Ive been really trying for this. I tried nulldc and it doesn't read and chankast does seem not to work I watched the to how to on youtube and now I think im missing another download or something and I don't understand. The site im using is Emulator Zone for this I have windows 7 so maybe that has something to do with it but my Game boy advance emulator works just fine on it. So please if anyone can help please I need like step by step instructions. any help is welcomed and appreciated Thank you for your time