If you add Products.OpenXml to your instance eggs and set it to Plone, you can index modern Office formats, at least .docx and .xlsx. For regular old Excel files (.xls) this does not work.
I tried it in the Plone 4.3.2 buildout configuration a few weeks ago:
[instance]
eggs =
...
Products.OpenXml
[versions]
lxml = 3.3.3
Products.OpenXml = 1.1.1
Products.AROfficeTransforms. Products.OpenXml, Product.AROfficeTransforms , excel,.xls. :
[instance]
eggs =
...
Products.AROfficeTransforms
[versions]
Products.AROfficeTransforms = 0.11.0
, xlhtml. , 2002 . .