If you go to this Holt textbook link
http://go.hrw.com/gopages/ma/msm3_07.html and click on homework help, you can see the same videos that appear to be in that Thinkwell site (and it's free), as well as practice problems.

These are the videos that DD is supposed to watch for school, but I think they are fairly idiotic. You can take a look, though.