Shame - no answer to your query yet so I've come out of lurking mode to try to help.
It's not about text to speech readers (screen-readers) working with the e-book, it's about how the pages are encoded. No hooks, gizmos or add-ins are required in the e-book - no wonder silence from Activ then. Accessible web design is a huge subject and, if you're really interested, send me an e-mail and I'll give you some pointers to web resources on the subject.
It's hardly surprising, given what my charity does, that I've worked with screen-reading technology and have designed/developed accessible web sites for longer than I care to remember. I have thrown various screen-readers at an e-book recently compiled in Activ. The pages are encoded in XHTML and CSS, are fully accessible to screen-readers and, with one exception (see Connect Outloud), work exactly the same in the e-book as on a web site. This is what happens with the screen-readers our clients use most:
Microsoft Narrator (the on-board software to which I think you allude) makes no claims for being a fully functional screen-reader, but it will read single column or single vertical div pages with no problems. Throw in more than one vertical column or div, however, and Narrator just reads from left to right across the page.
JAWS works perfectly on well designed XHTML or HTML pages, whether using CSS or tables and tag soup for layout and formatting.
Window-Eyes, the same as JAWS
Connect Outloud is a shortened version of JAWS, with less functionality and it does not work with all MS applications. It works perfectly with Internet Explorer, BUT it does not recognize the file-type for an "Activ compiled" e-book. So, even though the book sits inside a short-form IE, Connect Outloud will not notice and will ignore it.
Hal - this software is an enigma (aka a bit flaky) and you can't always be sure what is going to happen. The developers tell me it is optimised to work on table layouts - ironic really as Web Designers are fast moving to table-less (and frame-less) layouts. We've found a way round it but had to revert from a table-less layout to using one table and one table row inside each layout div - just for our e-book readers.
Don't hesitate to come back if you need more information.