I always use these instructions and install from source - www.theopensourcerer.com/2012/12/how-to-install-openerp-7-0-on-ubuntu-12-04-lts/

they are for ubuntu but should work for debian as well. i will test it out on my spare pi when I get a chance and follow up. (I assume you are using raspbian?)

<edit> I could not post the direct link because I don't have enough 'karma', so maybe if this helps you could give me some? </edit>