It is rather hardcore, but it gives you an idea of all that's involved.
I skimmed the link you gave. That, at least to me, over-simplifies the process. There are several spreadsheets on the net that you can plug the parameters into and get a crossover from.. however, it's all "theoretical", grounded in science, but won't usually exactly mirror the real world. When you get to the actual drivers, they behave a little bit different then the spreadsheets say.
I'm waiting for a buddy of mine to find some time and we're going to build my first from scratch crossover. My tools -- an LCR meter, a testing mic and and RTA. I plan on using the spreadsheets as a starting point, then tweaking based on the measurements and my (flawed) ears.
Also, a premade crossover, unless it's designed for the speaker drivers you have, WILL work, but PROBABLY won't give you a "good" result. It works along the same lines as the spreadsheet crossover.