Hello, you can use raspbian (Debian derivate for raspberry), and open erp should work, i cant post links but just search for "Raspbian open erp" and you should get more information.

I use debian and i just install postgresql from synaptic, and after that openerp, but firs of all you need to add the source... i dont know if its the same way for raspbian (Because of the different processor), but you can try.

Greetings!