Ufff, it is a very difficult question to answer
You are asking for a radiography of spanish society.
I would say that social classes are pretty similar to those in USA. There are differences, but perhaps less than in the USA.
Unemployment is quite high (10% aprox.) and salaries are lower (as well as prices) and vary from 9,000 € (an euro is more or less equivalent to a dollar) for a very bad paid job to 120,000 € which is the salary of a CEO of a medium company. Of course there are higher salaries, but we are talking about what is considered "normal".
The definition of class in Spain could be a mix of wealth and education/culture background. Lower classes are formed by not qualified workers. Higher classes are formed by wealthy people, the aristochracy and the richest burguesy.
Rising to another class is "easy" since education is free or very cheap in the case of University. We have a good social system to protect the less favoured. Our health system is "free" (payed via taxes) for every citizen, and we have an unmeployment secure, and a "salary" for life when your reach 65 years-old.
Inmigrants usually fall into the low class due to their situation (though some are starting to rise thanks to their businessess). Gypsies fall in the low class in their majority due to lack of integration (as always, there are exceptions).
Until ten years ago Spain was pretty homogeneous. In the last ten years we have received 3-4 million inmigrants, so ethnic differences (save gypsies) are only caused due to peoples inmigrant condition.
Fernando