This code works for me, and this is pretty much taken directly from the 6.1 code from what I recall:

from openerp.osv import osv,fields

class launch_map(osv.osv):
    _inherit = "res.partner"

    def open_map(self, cr, uid, ids, context=None):
        if context is None:
            context = {}

        partner = self.browse(cr, uid, ids[0], context=context)
        url = "http://maps.google.com/maps?oi=map&q="
        if partner.street:
            url += partner.street.replace(' ','+')
        if partner.city:
            url += '+'+partner.city.replace(' ','+')
        if partner.state_id:
            url += '+'+partner.state_id.name.replace(' ','+')
        if partner.country_id:
            url += '+'+partner.country_id.name.replace(' ','+')
        if partner.zip:
            url += '+'+partner.zip.replace(' ','+')

        return {
            'type': 'ir.actions.act_url',
            'url': url,
            'target': 'new'
        }

In your view, just add a button on the partner that calls the open_map function. No more complicated than this:

<openerp>
<data>

<record model="ir.ui.view" id="view_partner_form_googlemaps">
    <field name="name">res.partner.form.googlemaps</field>
    <field name="model">res.partner</field>
    <field name="inherit_id" ref="base.view_partner_form"/>
    <field name="arch" type="xml">
        <xpath expr="//sheet/div[@name='buttons']" position="inside">
            <button name="open_map" string="Google Maps" type="object"/>
        </xpath>
    </field>
</record>

</data>
</openerp>

You can just add in your additional fields wherever they're necessary to fill out the address format in a single line, Google will take care of the rest.