Okie doke. I took my week off for my back. And I just got back from doing legs. The 2 sets I have to show are the same weight as my video up above, but boy I was breathin heavy on these ones

I hope the form is better on these ones.
[youtube]http://www.youtube.com/watch?v=9ZREG7b1kw0[/youtube]
[youtube]http://www.youtube.com/watch?v=g1KNsRaLeZA[/youtube]
although on the final set tha stiffness in my back started coming back again, is it because Squats also work out the lower posterior chain as well?
It looks to me like your using far too much weight for a start, use less weight and concentrate more on form.
As for your form;
You do not go deep enough by far, these squats look like partials!
You want to be going atleast to parralel, but it is better to go beyond that in my opinion.
Your knees come too far forward and need to follow the lines of your toes and finally you need to stick your backside out more!