How does a driver move from the Nationwide level to the Sprint Cup level?

by driving the wheels off the damn thing

The easy answer to your questions I believe is that the track and performance decide who goes where. if you have a fast enough car to get into the field, then your in. However, the other answer kind of depends on the team that a certain driver is on. Many of the Sprint Cup teams nowadays have what could be likened to a farm system in baseball. This means that they have cars in all the series, including ARCA and the many "home tracks" that NASCAR touts. So then it would depend on how you do for a certain team and whether they have room or a space to fill for you to move up. Of course their is still quite a bit of the old way of doing things. That means that if you can get into a car and drive the wheels off it and the right people see you doing so, they will offer you a deal with their team. To answer your last question, I think that on track performance decides who is good enough and who isnt.

talent, most of the time. that and sponsorship dollars come into play in the decision. the two polar opposites: logano is coming up to nationwide once he turns 18 (next week) not only because he is a jgr development driver because of his talent. and i spoke with someone at jgr's store last week, and he said they haven't been making any "logano wear" as they haven't lined up sponsors for him yet. or that's what i thought he said.

on the other end of the spectrum, david gilliland came up from natiowide to cup because he was the first (and one of the few) nationwide only drivers to win a race that year. he was thrown into the deep end of the pool too soon - made obvious by the number of DNFs he managed to rack up (and how many other drivers he wrecked) when he was called up to "the bigs."

They have to get really good consistant finishes and then that usually attracts Cup team owners and then the driver has to sign a contract.

Talent. If they are winning in Nationwide, they will have the money behind them to break into Cup (or at least try to qualify for a race)..

They also have to be "approved" by some committee. There's an article at nascar.com about that very thing but in relation to like the IRL guys coming in.