install.packages with R 2.9.1 under Vista?

     What do I need to do to get "install.packages" to work properly for 
me in R 2.9.1 under Vista?

     Currently, install.packages in Rgui 2.9.1 by default goes to 
"C:\\Users\\sgraves\\Documents/R/win-library/2.9".  This is a problem 
for me, because R running under Emacs does not currently look there.

     I made the mistake last night of first installing R 2.9.1 in the 
default "C:\Program Files".  When I found that packages I installed 
using Rgui could not be found from within Emacs, I uninstalled R from 
"C:\Program Files" and reinstalled it under "C:\Users\sgraves\R" 
alongside R 2.9.0, which has allowed "install.packages" from Rgui to be 
accessed from R under Emacs.

     I've traced the problem to the different behavior of ".libPaths()":

*** Rgui: .libPaths()
[1] "C:\\Users\\sgraves\\Documents/R/win-library/2.9"
[2] "C:/Users/sgraves/R/R-2.9.1/library" 

*** R under Emacs: > .libPaths()
[1] "c:/Users/sgraves/R/R-2.9.1/library"


     What do you suggest?      Thanks,