Heya, just wanted to ask a couple of questions/see if I could get a problem addressed.

I am just starting "starting strength" program, a couple of weeks in.

I have watched a lot of videos on form and there is a lot of minor contradictions, most people seems to disagree with Rippetoe who says to keep your head at a downward angle while squatting (the tennis ball under chin method), like this guy says for example:
http://www.youtube.com/watch?v=EkF9Q...layer_embedded
(so you think you can squat)

Rippetoe says it helps with hip drive, others seem to think its bad. Thoughts?

What about lower back? I don't remember any mentioning of what to do with lower back from Rippetoe, besides some incomprehensible stuff on overextension. What to do with lower back?

My squat seems to be stalling fairly fast. I noticed last time the weight moved slightly forward coming up, and I did a slight amount of the "cat box" movement trying to get the weight up on a rep. I have a hard time "pushing" the bar down further on my back to a low-bar position, I think my shoulders are inflexible, so I have been mostly doing high-bar-- but I feel like the center of mass of the squat is moving forward and throwing me off.

I feel my knees coming inwards slightly on tough reps, and sometimes I get an odd twitching in my left ankle which throws me off.

All of that said, I have had a few knowledgeable people sweat my squats and say I had surprisngly good form for a beginner, I was doing lighter weights at that time, so I think my form is good for easy weights and I start to break form when the weight goes up. This seems standard, but I obviously want to fix it.

cliffnotes:
Head position?
lower back, whatitdo
how to fix weight moving forward, knees buckling inwards?

Thanks :P

I think Rippetoe advises to keep your head/eye at a lower angle because it is a low-back barbell squat. If you are doing high-bar, like in that video, you want to keep your head and eyes parallel or slightly above. Also in high-bar your chest will be "proud," and your back angle will be more vertical.
I am not sure what you are asking about lower back. IIRC, Rippetoe talks a lot about keeping it tight and goes into some depth concerning this. He has the noob get face down on the floor at gets them to isolate these muscles by doing a superman type thing so they can feel how the muscles should be working while squatting. Not sure what you are wondering about.
For me, low-back has too many issues to be worth it for general strength training. I am sure PLers have a more nuanced view on this. I just don't find the position comfortable, it hurts my shoulders, and it doesn't seem to engage my hamstrings or posterior chain in a much more significant manner to make it worth it.
Also, of course, I may be wrong about some or all of the above, just my opinion.