Cost distance analysis

Hi Chrissy:

I have had similar needs in the past, so I did some searching: The R 
package e1071 -

 http://cran.r-project.org/web/packages/e1071/index.html

..includes a routine for computing the shortest path distance matrix.

You might start with this package....

Or, the GRASS vector routine v.net.path might work for you.
There is a good data interface between R and GRASS: see the spgrass6 
package.

Rick Reeves