Don't know what games, there has to be specific set of circumstances to really evaluate because Posey guarding Kobe during a span when he's really not looking to dominate is pretty much useless for our purposes.
But here are some highlights from a game against the Hornets, I didn't watch the game and don't know the circumstances, but there's one or two plays which illustrate what I was pointing out of Kobe blowing by Posey. The important part is looking at the foot work and the speed. Also interesting to notice that later in the highlights Posey is guarding someone else (until the last play)... don't know if it was because of a defensive switch or because they simply decided to take Posey off Kobe.
http://www.youtube.com/watch?v=lUd3oTIY4VINot the best example, but something worth looking at for our purposes. If Posey guards him aggressively, he's too slow to keep up with him. He needs to give him some space, and Kobe is a pretty good jump shooter.
Edit:
Here are some highlights from Game 3... there are a couple of plays of interest. Not the best examples, but it gives an idea:
http://www.youtube.com/watch?v=nlZfZk5jg-I&feature=related