the following taken from a thread entitled “Emacs won’t start with ESS” in August 2009 of the ESS list started by Gustavo Lacerda.
if u want to use emacs to find a directory or file on your system, try M-x find-dired. example: M-x find-dired / -name ess-site.el
if u want to find an emacs library in your path, try M-x locate-library ess-site.el .
wow emacs is so useful!