Why are you wanting to "cascade" style sheets?
As I understand it, the idea of style sheets is to set up certain display attributes that a web book (multiple web pages ... my own bs term of the moment) can use to mantain a consistent style ...
I messed with this a year ago or so ... and found most of the tags to be very buggy... some worked only for netscape, others only for IE... others didn't seem to work in either... I lost interest...
I don't know anything about dreamweaver...
All I can offer is that you style sheets can take the attributes of the parent style sheet and can add or override attributes. In this way you can have global style sheets for the entire site, and then you can "cascade" the style sheet with another style sheet that will add to or modify the attributes for specific tweaks to sub pages...
I personally dont' care for them....
This will also move the question up for someone who does actually like them.