This answer helped me toward a solution that worked for me. I was trying to compile a 32-bits version of boost_1_43_0 on 64-bits debian and eventually came up with this:
./bjam \
cflags=-m32 \
cxxflags=-m32 \
address-model=32 \
threading=multi \
architecture=x86 \
instruction-set=i686 \
stage