How to warm up / stretch and cool down? I'm starting to ride again after a couple of years of not doing any sports at all. I dimly remember some stretching exercises back from school, but I don't know if I'm doing it right at all.

Instead of listing what I'm doing and asking for "correct, yes/no", I'd like to know how exactly one should prepare for a bike tour. I'm currently doing small tours (20km) to get used to it again, but plan to go bigger during summer.

Just a few minutes ago I stumbled upon the following article, explaining a few stretching exercises. Unfortunately, it's focused on running, and I believe that there aren't exactly the same muscles involved.
Five Fantastic Stretching Exercises (pdf).

The article also mentions a cool-down phase, which I don't remember at all from school.

So, to conclude: How should I warm up, how long, what stretching exercises should I do, and when? How should the cool down be done?
Stretching has become somewhat controversial among exercise physiologists.   I listened to one such lady on NPR's Science Friday a couple of months ago, and she said that the university she worked out of had conducted a number of fairly extensive tests and surveys indicating that very little benefit accrued from this practice.
Other than that it felt kind of good. Wired's Pre-Exercise Stretching Is Killing Your Workout article discusses such studies.

I've never bothered with pre-ride stretching.  In fact, the standard wisdom is that one should first warm up and THEN stretch.
Ride slowly, let the legs get used to spinning and the arms used to bearing a bit of weight before increasing your pace.
I used to stretch post-ride; the standard quad and hamstrings stretches and also calf-muscle stretches by standing with my toes on a stair and letting body-weight stretch the calf... But I admit I hardly bother anymore.