Things you'll need to do this:
1. A real Dreamcast (to read the original game discs)
2. Either a broadband adapter for that Dreamcast or a serial cable to connect it to a PC
3. A router (if you have to use the broadband adapter because you don't have a serial cable)
4. Some special apps to perform the "magic"
5. Google to search for a guide on how this is done (since this type of discussion is not allowed on this forum)