The reason Krista recommends 45lbs is because a standard Olympic barbell is 45lbs (well, 44.something) - so she is recommending you start with the empty bar. This is just IMO but cheap barbells that come in 20,25lbs are just not worth it for real lifting. There are some high quality women's bars at 35lbs (with a smaller diameter for smaller hands) if you wish, but 45lbs is the minimum weight for proper barbell usage. You can't go lower.
60-70lbs is fine to start (heck I started with 2x20lbs I think and now I've 600+lbs of Werksan plates... nope, not all once hehe) however you'll want to get a proper squat rack as well.
If you aren't sure where to start, just go with the regular bar for squats (44lbs) and the bar with proper sized bumper plates for deadlift - the plate quality is important because you are deadlifting plates that are a proper size. If you try and deadlift with those "mini" plates, your back will be going down farther than it should and make the lift akward.
This is where I buy my plates
^^The bumper plates can come in 2.5-5.0kg and are the same size as a 45lb plate, just (obviously) heavier. Believe me, that is one small difference that can make a huge impact when trying to learn the lifts.
Startingstrength.com by Mark Rippetoe has an amazing book and DVD, IMO, you should never touch a barbell without! I highly recommend it.
Here are some Youtube videos of his