The same people, Versus Books, that did the Dreamacast version also did the GC/X-Box. In fact, they just copied and pasted their old work, added a few pages of new content, lied a little bit, and sold it as a new strategy guide! It's no wonder they don't exist anymore...
Good luck finding the strategy guide, though. If you can find the Dreamcast version, it's almost exactly the same, word for word...