Idea 1) First of all, this idea is untested! Its not simple and requires some knowledge of postgres and creating own openerp moduls. The idea: Use postgres foreign data wrapper to connect to the mysql database tables. So you have all your tables from mysql in your postgres database. Then you create own models, with an ORM that reflects your mysql tables, define the proper fields for every column and so on.

Idea 2) Create the datastructure of your mysql database with an own module and write a data copy script to import your data.

In the next step (no matter which idea you chose before) you can define reports based on those ORM or define views on those other tables.