Not to worry - there are a lot of ways to do that. These methods, however, require your users to be online everytime they open your ebook:
1) easiest way: make all your page links directly to web pages you post on your site (unavailable to casual surfers).
2) almost as easy: create pages for your ebook that redirect to your online pages.
3) also easy: create your pages with most of the styling, but deliver the online content into iframes. This will display a mix of ebook and online content.
IntroParagraph="Welcome to our Real-Time eBook! This ebook was last updated on ";
This_Info_LastModifiedDate="October 5th, 2004";
ListofProducts="Widgit 1<br>Widgit 2<br>Widgit 3<br>......";
TableofPrices="<TABLE COLS=3><TR><TD>Product</TD><TD>List Price</TD><TD>Your Price</TD></TR><TR><TD>Widgit..."
Then, when a user opens your ebook, the fields within will fill with these values - found online in the .js file. You could even write the updated information to a file on the users' machines, so that if they aren't online, they will still have the last updated information from the most recent online visit in their ebook. Active provides for this, and I have a demo on how to do it; I've posted a zipped activ project with a form or two here:
It demos using a form to get information, and how to write and read a file. It might suit your purposes - you wouldn't have to use the form part, just writing the local .js file, and reading back it in.
Hope this helps -