libR.so: cannot open shared object file

Can you add some details?
Suppose i have the package Model.tar.gz and my writable are is in user/area, 
what i have to do next to install the package?

What I was picturing was something like this (forgive me if syntax isn't 
100%):

mkdir user/area/myRLib
R CMD INSTALL --library=user/area/myRLib Model.tar.gz

and then in R:
library(Model, lib.loc="user/area/myRLib")

Note though Brian Ripley's response to me where he indicates that this is 
handled automatically.

-J