The main issue addressed in this paper is how to help learners plan a navigation path in existing web-based learning resources, which is an important process of self-directed learning in hyperspace. Our approach to this issue is to provide learners with the adaptive preview of a sequence of web pages as navigation path. Following the idea of path previewing, we have developed an assistant system. The system displays an overview of a web page selected by learners from a hyperspace map, by extracting information from the HTML document file related to the navigation path-planning context. It also enables learners to transform a sequence of previewed pages into a navigation path plan.