The text of powerpoint files is indexed if you have the OpenOffice server running - which is used by Alfresco to index certain types of documents. There is a known problem with OO 2.0.2 in which transformations/indexing is not working, and some users are reporting some issues with 2.0.1. Therefore I would suggest using OO 2.0.0 for now to make sure your powerpoint docs are being indexed.
Hope this helps,
Kevin
