The leg press has helped with my ability to squat. Today I did 245 on the leg press and I feel much better trying to squat down without any weight (or bar). Since the leg press is at a 45° angle and I weight about 240 lbs, I'm figuring I need to work up to csc(π/4)*240 ≈ 340 pounds.
I've also been trying to work on my squat grip, holding the bar properly and whatnot based on Mark's
video.
It was a good day today. I know you guys might not like all of this stuff I'm doing to build up to it, but my knees are really in that bad of shape.
As a beginner myself who tried this a few years ago, IMO what you're doing is fine. Everyone here says to start with the bar and avoid the machines, follow the book and you'll start squatting properly... but it's not quite that simple. If you've lead a sedentary lifestyle, you simply can't internalize what you're seeing on a video or reading in a book to make your body do exactly that. I tried all of that, including posting videos of myself for suggestions, but in the end I ended up with lower back trouble.
IMO the best way to learn the squat is to have a professional who's trained in SS teach you how to do it (note that most fitness instructors have a very different idea of what a squat is when compared to the book). You can give the video/book etc a shot and it might work for you, but ultimately I stopped doing them because I was just too scared of lower back issues (and I had other logistic problems as well.)
Not to put a damper on your workout - I think SS is a great program, if you can follow it precisely. But if you're used to a sedentary lifestyle, I'd recommend taking it slow and doing things that make your body feel comfortable. There's no point in injuring yourself and not being able to do *anything*.
As for a slower, "lead in" program that doesn't have you be a purist, try the beginners workout on
http://exrx.net. I'm trying that currently, and while it does include compound lifts, you don't get judged if you substitute a machine workout for something you find hard to do. I'm having a great time doing it - especially in terms of time taken for workout and how I feel afterward, and in strength/fat loss gains. Pay particular attention to the "mobility exercises". I would recommend doing this for six months and then doing an SS style program where you focus on progression through heavy weights and low reps.