I have to admit to having only tried The Illinois Accessible Web
Publishing Wizard for Microsoft® Office http://www.accessiblewizards.uiuc.edu/ which costs around £28 and is very
simple to use as an extra menu item within PowerPoint and you can adapt
the results to suit your needs. I have examples on the LexDis website http://www.lexdis.ecs.soton.ac.uk/presentations/