in mariokart wii, how do you unlock rosalina and what is the wii cup series ?

if you have super mario galaxy all you need to do is to race 50 race and you will unlock her!

From youtube user:
In order to unlock her, you would have to:
Mirror Grand Prix: Score * or higher in all cups or, Play 50 games and have a Super Mario Galaxy save data, or play 4,950 games.

Also there is a vid on youtube saying that you can unlock without Mario Galaxy too

this site will give you a nintendo wii just for completing some quick online tasks! really recommend it, especially if you're broke but really want a wii (like me).

u have to have a saved file in super mario galaxy. then u just race and u unlock her in the 50 cc or somethin.