package installation fails only for "sp"

I have escaped Splus for Windows (mostly) and have started using
R (v 2.3.1 on i686 redhat).  Installing packages has been routine except
for "sp" (classes and methods for spatial data).  I get the following error
message

 > install.packages("sp")
Warning in download.packages(unique(pkgs),destdir=tmpd,available=available,:
            no package 'sp'  at the repositories
 
Clearly I am missing something (probably obvious), but can someone 
enlighten me
as to why the behavior of this package installation is different from 
others?  sp is
listed under "Contributed packages" at the R-project URL.  Thank you
for your time.

___________________________________

Don McKenzie, Research Ecologist
Pacific Wildland Fire Sciences Lab
USDA Forest Service
400 N 34th St. #201
Seattle, WA 98103, USA
(206) 732-7824
donaldmckenzie at fs.fed.us

Affiliate Assistant Professor
College of Forest Resources 
CSES Climate Impacts Group
University of Washington
dmck at u.washington.edu