The first method used an exploit found in the game Phantasy Star Online, basically, the method consisted on using the Dreamcast itself to read the GD-Rom and stream it through an ethernet cable connected to the computer.
The second method consisted on the typical disc swapping. It worked by introducing a CD filled with data on your computer, and swapping it with a GD-Rom without your computer knowing it. That way the PC thought there was data all the way to the end of the disc, due to it using the CD's TOC, instead of the newly swapped GD's TOC. This method produced a 1:1 copy of the disc.