You are incorrect!!
You have to use the special cable (DC to PC Serial cable), true enough. You must use a software package on the Dreamcast called Serial/Slave (or something similar) and a program called TerraTerm on the PC.
Once the game has been *RIPPED* from the Dreamcast, it is still not ready to burn to the disc. It must be extracted and downsampled and some features may have to be ripped out to allow the game to fit a standard 700mb disc. In addition, the game files must be hacked so they work on a standard CD-R.
If even one step listed above isn't performed or is performed incorrectly, the disc you burn won't work.
With that said, good luck if you decide to try. If not, 'tis a wise decision...