You need to use <div>
and <group>
tags.
Take a look at the way the Partner form view works.
Hijacking the pre-defined CSS div class address_format you can have something like:
<group>
<label for="degrees" string="Latitude" />
<div class="address_format">
<field name="degrees" style="width: 33%" />
<field name="minutes" style="width: 33%" />
<field name="seconds" style="width: 33%" />
</div>
</group>
You should also educate yourself about the <col>
and <colspan>
attributes.
https://accounts.openerp.com/forum/Help-1/question/1490
It worked.
For the record: one has to declare the form as 'version="7.0"'.
HTML tables are also allowed.
Thanks!