Here's the original How-To: Full YouTube on Windows Mobile post. The thread to download the necessary files that zbop created is here. You'll need to be a registered member of the forums in order to download, I'd recommending starting that here.
Hat tip to Mike over at Phone different for making the joke that inspired this video. As long as I'm referencing the iPhone, I should mention a couple things just so I don't get flamed into oblivion: Windows Mobile browsers stink compared to the iPhone's, as I've mentioned before; also - you'll need either a fast processor or to do some tweaking on a device with a slow one; yes, it's aggravating to have to deal with those sorts of settings; and yes - there's more lag than is strictly ideal.
So many caveats, so little time. Note how I artfully restrained myself from an infinite regression beginning with posting a video of me watching this video on a Mogul - that way lies madness.