Partner Labels and Product Labels are not reports that you can edit in the OpenOffice report designer. See here: https://accounts.openerp.com/forum/Help-1/question/5284/
The existing labels probably need to be changed and there could be a need to have different versions. Anything is possible for an OpenERP expert but for someone who just uses a basic tool like OpenOffice, what would be best way to create different labels?
You can create a new report using the openoffice plugin. In the 6 version you could use:
[[ (move_lines.product_id.default_code) and setTag('para','barCode', {'xdim':'10.0mm','height':'15.0mm','code':'code128'}) ]] [[ move_lines.product_id.default_code ]]
Something like this. Is this what you are looking for?