R help - May 2010 - connectivity analysis for spatial information: from raster to graph

hello...
I am trying to develop an analysis similar to the proposed by Urban
and Keitt (2001) for connectivity between patches in a landscape. To
do that, my first problem is to convert the raster map, into a graph
(with area of the patch as an attribute for the node, and the distance
between patches as the attribute for the edge).
Do you know of any function that can allow me to convert the raster
map and create the graph? and a package to realize such kind of
analysis?
Thanks in advance

Carlos Alberto Arnillas

Ref: Urban, D., Keitt, T. 2001. Landscape connectivity: a
graph-theoretic perspective. Ecology. 82 (5): 1205-1218