Recently, I have the need to extract some texts from a PowerPoint file at work. And I got to find out a website which provided a nice tip. You can also try this if you have a gmail account. Just simple mail the file you want to convert to your gmail account, then you can click “View as HTML” link next the the attachment. Hola! You got the text version of your files! Gmail supports viewing Microsoft Office Documents (Word, Excel, PowerPoint), PDFs, and RTFs as texts.

You don’t have a gmail account? You may ask your friends to give you an invitation to sign up!

I find the tip here: http://labnol.blogspot.com/2005/12/convert-doc-xls-ppt-rtf-pdf-to-html.html