My son is using a textbook that does not have an audio version (tape/CD) available. Is there software that will copy/scan and convert to audio?
Scanning and converting a text to audio can be time consuming and expensive, depending on the software you use. If you only need one textbook (and all of his other textbooks are available in audio format), it may not be worth it to purchase software for yourself. Start with Learning Ally or Bookshare.org; they often have textbooks available when you may not be able to find them elsewhere. If your son has a documented disability, he can access any books from RFBD or Bookshare.org.
If you cannot find his textbook through a source such as RFBD or Bookshare.org, or you think you'll need to scan and convert texts on a more regular basis, you may want to consider purchasing a scanner and accompanying text-to-speech software. What you end up purchasing will depend on your needs and how much you want to spend. Solutions for having text read aloud range from the incredibly simple - scanning in text and using built-in voices to read - to the more complex - scanning in text and using human sounding narration and converting to an mp3.
For example, Adobe Acrobat Reader and Microsoft Word both have very simple text-to-speech capabilities. If your son just needs to have the text read aloud to him while sitting at the computer, and doesn't mind synthesized speech, this could be a very basic solution. However, if you'd prefer something with more natural-sounding narration, you might need something with more features. Find a variety of solutions for scanning and text-to-speech in this customized search on the TechMatrix.