loading packages - mac user

Hi,
I'm using a Mac, I've downloaded R (base), and I'm trying to download
the package R Commander. I thought I had already done this (both from
the web and from within R) but it doesn't seem to be working - it's
not there as a "search()" reveals.

However, there are plenty of files
on my system linked with Rcmdr - located in
HD>Library>Frameworks>R.framework>Versions>2.1.1>Resources>Library>Rcmdr.
Is it simply in the wrong location to use it? The other possibility is
that I keep getting a tcltk error whenever I try to load up the
package from the Package Manager from within R - and when I try to
upload the tcltk package, this also gives the same error [1].

get a "Couldn't launch application" error whenever I try to launch the
X11.app.

This is probably so basic it's staring me in the eyes, but I need your
help please. I'd be happy to give any extra info you need.

Thanks
Cormac

[1] Loading required package: tcltk
Loading Tcl/Tk interface ... Error in dyn.load(x, as.logical(local),
as.logical(now)) :
	unable to load shared library
'/Library/Frameworks/R.framework/Resources/library/tcltk/libs/tcltk.so':
 dlcompat: dyld: /Applications/R.app/Contents/MacOS/R can't open
library: /usr/local/lib/libtk8.4.dylib  (No such file or directory,
errno = 2)
In addition: Warning messages:
1: cannot create HTML package index in: make.packages.html()
2: cannot create HTML package index in: make.packages.html()
Error: .onLoad failed in 'loadNamespace' for 'tcltk'
Error: package 'tcltk' could not be loaded