well you need the Dreamcast bios. [edited by moderator] Put it in (assuming you have a mac) /user/library/application support/lxdream. i believe the binary program they refer to is an emulated bios, not the real thing, i dunno though

Please do not encourage downloading of the BIOS rom - it's copyright SEGA.

Unfortunately, the BIOS is currently required in order to boot from a CD/GD disc. If you live in a country that permits format-shifting, you can dump the BIOS (and optionally your flash ROM) from your dreamcast using dcload and related tools. You then need to tell lxdream where the files are in the path preferences.

Otherwise you will only be able to directly run binary programs - fortunately most demos and homebrew are available in this form - from the "Load Binary" option on the file menu.

I'm currently working on a boot mechanism that does not require the BIOS, but it's not quite ready yet.