How to plot the dendrogram or tree for kmeans ?

Why do you think there is one?  kmeans is an agglomerative clustering
 algorithm, not a recursively dividing one.

 Since there is no clustering hierarchy, so there is no dendrogram.

However, you could create a "clustergram":

@article{schonlau:2002,
	Author = {Schonlau, Matthias},
	Journal = {The Stata Journal},
	Pages = {316-327},
	Title = {The clustergram: A graph for visualizing hierarchical and
non-hierarchical cluster analyses},
	Volume = {3},
	Year = {2002},
        Url = {http://www.schonlau.net/clustergram.html}
}

Hadley

http://had.co.nz/