Question:

Is it possible to reference an external HTML file for the contents of the AutoScroller, rather than have the actual HTML in-line for every page that displays the AutoScroller?

Answer:

Using SSI (server-side includes), it is very well possible to have the content for the scroller coming from an external file.

You'll find basic information about SSI at http://www.dwfaq.com/tutorials/dynamic/SSIs.asp, but a simple search in Google will return lots of links about this subject.