Recently, I began reading about agile methodologies and XP in particular. I am a bit confused, though, about what are considered the practices involved in extreme programming.

More precisely: Wikipedia reports 12 practices, which I someway believe to be the "classic" ones.

Both Kent Beck and Ron Jeffries indicate 13 practices (you can find the links at the bottom of wikipedia page about "Extreme Programming Practices", I cannot post them here since I am new user of Stack Overflow), while this review of Kent Beck's "XP explained" (2nd edition) report more than 20 somewhat different practices.

As a complete beginner in the topic (and basically as a complete beginner as a programmer), I would like to be enlightened on the matter. My impression is that I should look at Beck's book, since the second edition has been written after several years of XPerience, but I can find a lot less material based on that.