Rather than Microsoft-style windows that each confine a particular application, these would be windows within an application, windows that open into different aspects of a related cluster of information.
The windows could represent the paths open from this point, the options available for the next chunk to be consumed -- a preview. The size or shape or border of a window, or a text label attached to it, can provide additional information before the user leaps through the portal.
The windows might be independent of one another, or they might be linked to what is in the "active window" -- the one the user is concentrating on at the moment. Whenever the user brought something new into the active window, all the options in the peripheral windows would change. This would be especially suitable for the directed-search style of cybermedia use, in which the user would be researching a subject.
"Doors" could lead out of a cluster of related information and into another cluster, while "windows" could offer views into data belonging to the current cluster.
This echoes an idea expressed by Jakob Nielsen; he describes clusters of nodes arranged in mini-networks. This would mean grouping a number of closely related nodes, or chunks, together in a way that facilitated easy movement among them, with probably a more deliberate effort required for the user to exit from one cluster and go on to another.