More info and a Linux Port
Recently sega released a broadband (Ethernet) adaptor for the Dreamcast which contains a Realtek 8139 ethernet chip. This has allowed people to create boot CD’s that can be used to load and run software created on the PC much quicker than via the serial interface lead. If you’re new to Dreamcast coding then just get yourself one of the Broadband adaptors. A serial interface is still useful if you don’t own a keyboard+mouse for your dreamcast, and you can also use it to view debugging output from programs you run on your dreamcast.
Linux has also been ported to the dreamcast and there is already a fully working distribution of it available.