To work at Nordstrom, you first need to fill out an application. Put on the application that you want to work in cosmetics, and *prefer* MAC. Then get in touch with the department manager or assistant manager and find out if they have any openings, say you want to work in cosmetics. You could reverse the order of these first two steps and it wouldn't matter much. *Then,* hopefully the manager or assistant will set up an interview with you. This is when you mention that you really want to work for MAC...if they have told you there is an opening there. If they say there isn't, you should listen, and interview as if there were. Later, if you get offered a different position, tell them that you have given it a lot of thought and decided you really only want to work for MAC and you hope they will understand why you are turning down X position, and keep you in mind for MAC openings. If there *is* an opening at the time of your interview (and openings happen often and quickly in all lines) then go ahead and tell them that's the position you really want. Then if they like you, they will arrange a MAC interview for you, usually with the Account Executive or Coordinator, and possibly the Counter Manager. You may be asked to do a make-up application at this interview, or maybe one later...but you will almost certainly be asked to do one.
Things to keep in mind...if you are offered a different position, do not take it thinking you can move over to MAC soon. Nordstrom and most lines require you to commit to that line for at least a year. Unless it's a dire situation, Nordstrom will *not* move you until your year is up. And second, you will almost certainly not be offered full-time with MAC unless the store is very small. MAC has lots of part-time people and not that many full-time, so if you need full-time you may need to start in a different line, or plan to have 2 jobs while you work your way up in MAC.
It's never a bad idea to befriend the Counter Manager at the counter you want to work for. She can tip you off to when there are openings and it's a good time to apply, and can talk you up to the manager/assistant.
I hope this helps!