You don't need to "call" the other style sheet - you simply name it stylesheet_ie.css and zen will automatically pick it up and apply the differences.

Zen has a text pad in the css folder called css read me I suggest you peek at it.

Basically, zen will read stylesheets in alphabetical order in the css folder so if you have :

stylesheet.css
stylesheet_ie.css
stylesheet_mine.css
stylesheet_new.css

Zen is going to read and apply those stylesheets in exactly that order.


Hope that helps