Using Makefile in my package

I am trying to create a Makefile for my C source code in my library.
Yet, whenever I try to build the package I get:

$ R CMD build spatrr
* checking for file 'spatrr/DESCRIPTION' ... OK
* preparing 'spatrr':
* checking DESCRIPTION meta-information ... OK
* cleaning src
make: /Library/Frameworks/R.framework/Resources/etc/Makeconf: No such
file or directory
make: *** No rule to make target
`/Library/Frameworks/R.framework/Resources/etc/Makeconf'.  Stop.
* removing junk files
* checking for LF line-endings in source files
* checking for empty or unneeded directories
* building 'spatrr_1.0.tar.gz'

I've noticed some older posts pointing out that references to Makeconf
should be $(R_HOME)/etc${R_ARCH}/Makeconf, but everywhere I look this
seems to be setup correctly.

I am using the standard binary download of R 2.5.0 on OS X 10.4.

Thanks in advance for any help!

-- 
To know that we know what we know, and that we do not know what we do
not know, that is true knowledge --Henry David Thoreau (quoting
Confucius): Walden