Error loading packages, command 'tar' missing from path?

Hello all,

My appologies for any possible cross-posting--I originally posted a  
version of this to R-Help, but was refered to r-sig-mac because  
apparently my problem is mac-specific.

I'm running R2.8.1 on a Mac OS 10.4.11.  While trying to install the  
package gdata, I was presented with the following (error at end of  
report):

install.packages("gdata")

also installing the dependency ?gtools?

trying URL 'http://cran.stat.ucla.edu/bin/macosx/universal/contrib/2.8/gtools_2.5.0-1.tgz'
Content type 'application/x-tar' length 85484 bytes (83 Kb)
opened URL
==================================================
downloaded 83 Kb

trying URL 'http://cran.stat.ucla.edu/bin/macosx/universal/contrib/2.8/gdata_2.4.2.tgz'
Content type 'application/x-tar' length 539301 bytes (526 Kb)
opened URL
==================================================
downloaded 526 Kb

/bin/sh: line 1: tar: command not found
2009-03-02 20:42:06.081 R[357] tossing reply message sequence 3 on  
thread 0x1ce3ae0
Error in sprintf(gettext(fmt, domain = domain), ...) :
 argument is missing, with no default


It seems that 'tar' is missing which (I'm guessing) leads to an  
error in sprintf().  I've never been presented with this error  
before.  I tried loading various other packages and received the  
same error.  When the error first appeared, I was running R2.5.3.   
After upgrading to R2.8.1 the error persists.

Thanks in advance for any help--
Andy Rominger