[R] package installation on Mac OS X 10.3.9

[Patrick Giraudoux]

Dear listers,

I am tryin to install a package in a student training room. 
Unsuccessfull! With this message:

 > install.packages("pgirmess")
trying URL `http://cran.r-project.org/src/contrib/PACKAGES'
Content type `text/plain; charset=iso-8859-1' length 77400 bytes
opened URL
==================================================
downloaded 75Kb

trying URL `http://cran.r-project.org/src/contrib/pgirmess_1.2.5.tar.gz'
Content type `application/x-tar' length 49962 bytes
opened URL
==================================================
downloaded 48Kb

ERROR: failed to lock directory 
'/Library/Frameworks/R.framework/Versions/2.0.1/Resources/library' for 
modifying
Try removing 
'/Library/Frameworks/R.framework/Versions/2.0.1/Resources/library/00LOCK'

Delete downloaded files (y/N)? N

Can anybody advise a bit more clearly about the origin of this failure 
and anticipate a way to work it around?

Cheers,

Patrick