It seems that the current python 2.5 distribution does not include the struct module as part of python-core. In python2.5 the struct module is implemented by struct.py and by lib-dynload/_struct.so but the python manifest does not include struct.py and has struct.so instead of _struct.so. I've attached a fixed python-2.5-manifest.inc , it's only a small change in the python-core section. This problem was in the general OE distribution but was fixed sometime in November.
PS This is my first patch submission ever so please let me know if I need to do anything else.