Strange, I can't seem to reproduce the problem here with Ubuntu 10.04. As of Python 2.7.1, _weakref became a builtin, so not sure why it's trying to load it.
Did you download the source and run 'configure', 'make', then 'make altinstall'?
What you you get if you type 'python -v'?
What you you get if you type uname -a'?
I'll look into setting up 12.04 32/64 bit virtual machines in the meantime.