Dreamwidth style system discussion

OK, this one is beyond me. I can't figure out how the styles system creates different stylesheets, let alone how to tell it to do multiple different ones.

Specifically, I want to have a different sheet for screen media as well as one for all users (ie colourscheme goes for everyone, but put this box next to that one should be for computer displays, not mobile devices and similar).

Wordpress does this for the complete stylesheet:
link rel="stylesheet" href="http://s1.wp.com/wp-content/themes/pub/p2/style.css?m=1289584311g" type="text/css" media="screen"

But I want to do it in different sheets, this is partially for bandwidth purposes (my mobile contract has a large, but limited, DL limit) but also because some mobile devices and browsers get really confused by all-in-one stylesheets, Opera Mobile tries to ignore stuff it knows won't display properly (but can't always manage it, Blogspot blogs are worst for this), but a Palm Pre, I'm told, will try and put everything in the right place and shrink it, making DW unusable with styles on for a such a device.

So, two questions, one, how does the Styles system know which bit of the layer should create a separate sheet. Two, how do I figure out what the URL would be for each separate sheet in order to embed them for display properly?