OpenERP IOError: decoder zip not available
You can solve this by uninstalling PIL but it's a bit like preventing fillings by pulling out your teeth; you solve the immediate problem but...
The IOError you are seeing is usually because PIL can't handle jpeg images.  This happens because PIL is using hard-coded library paths.
To fix (on Ubuntu 12.04)

pip uninstall PIL
sudo apt-get install libjpeg8-dev
sudo ln -s /usr/lib/x86_64-linux-gnu/libjpeg.so /usr/lib
pip install PIL 

Note the output at the end of the PIL install, it will tell you which image types it is now handling.
I have installed openERP 7 multiple times on my Ubuntu 13.04 machine.
I am unable to create new user in openERP 7. When i try to create new user it shows message 

IOError: decoder zip not available

Unable to post complete output of the Error message.
I have already installed all required python packages. But have not solved it yet.