This page describes how to build an adaptor for the Dreamcast serial port that will allow you to connect it to any computer using a standard 9-pin DSUB connector. The main component is a MAX voltage converter, since the Dreamcast serial port uses CMOS (3.3V) voltage levels, whereas normal RS232 uses +/-12V levels.
This serial adaptor has been designed, built and tested by me. It works prefectly for me, but I will not be held responsible if it fries your DC, your computer, and/or your hair. Also, please note that you will probably only find this interface usable if