Quick How-To XC Ski YouTube (not by me)
Here's a YouTube vid that gives a great, quick look at how to acquire the essential goodness of XC. It's by Keith Nicol, of the Canadian CANSI.
I reviewed all the other how-to vid's online and didn't find anything, really, of worth, except this one.
Hint, hint: the main tip in general, and in this vid, is to ski without poles. Swing the arms, get complete weight transfer, then try slight uphills (also without poles) and notice that you have to drop down a bit and shorten up to keep getting that tasty grip and glide...
(Nudge, nudge: I plan on making a vid myself, covering the whole range, quickly and effectively. It doesn't have to be so hard. I'll try to show how to make it easy. A few core ideas is all it takes. For now, the following is the best! And, of course, the proof is in the pudding.)