Well, in the .c I commented out the #include<malloc.h> -- you don't need it, it's included in stdlib.
For the Makefile, I stripped it down to this:
topixmodule.so: topixmodule.c
[tab] gcc -c -O2 -I/Developer/SDKs/MacOSX10.3.0.sdk/System/Library/Frameworks/Python.framework/Versions/2.3/include/python2.3
-o topixmodule.o topixmodule.c
notice -shared is not there, it's not supported in OS X. so as an example I output to a regular old object file. you can play with libtool on your own. (man libtool).