I have built LAMMPS on my Mac with Snow Leopard, and it is pretty straight-forward. I use the make mac_mpi, and edit the CCFLAGS line. It should look like this:
CCFLAGS = -O
(i.e. remove the -MMD -MG flags)
Unless you want to use the particle-particle particle-mesh (PPPM) option, you do not need to have the FFTW library installed. But if you _want_ to have the FFTW available, make sure you have installed the FFTW 2.1.5 using fink.
To make LAMMPS _without_ FFTW, just edit the FFTW-line to "FFT_INC = -DFFT_NONE" in your makefile, and remove any other flag on that line. Also, remove the flags on the "FFT_PATH" and "FFT_LIB" lines.
Christer H. Ersland.