Does anybody know of an add-on or something that can change the appearance of section markers in Inventor .idw drawings?  I could make sketch symbols but would have move them everytime a section moved.
Detail markers also.

What do you mean by 'section markers'?
section lines? section layer? arrows?
Most of your problems can be solved via the manage tab, styles and standards, styles and standards editor.
but before that you must make your style liibrary from read only to read-write:
before you open anything, clicky file menu, projects
in open dialog box, use styles library-read only. right clicky read only, click yes.
save.
open your idw.
 

By section marker I mean the symbol(s) that define a section cut on a drawing. The default Inventor style is a chain line with arrows marked 'A' etc. on the parent view and a view title 'SECTION A-A' on the child view. This is according to various drafting standards and is correct for mechanical detail drawings, unfortunately I am doing structural engineering drawings and the section child may be on a different drawing to the parent so we use section marker symbols showing direction of cut, section No. and drawing reference to locate the section in the drawing set. Similar to architectural drawings. I know I should probably be using Revit but I love the modelling capabilities of Inventor and I don't think the company will get me a license anyway.
I have looked in the style manager (Inventor 2008) and have found that the Section View line and Detail View callout default object styles can be set to a choice of 'Miscellaneous Object (ANSI) or (ISO)'. I wonder is there a way to create new or modify existing default objects? I personally don't mind the way inventor does this but I'm trying to get Inventor to conform to company CAD standards.
 
 

So am I. And thats what it was made to do. Be customized.
You can definetly create your own, only problem with that is you have to import it into each drawing (or attach once, to a template), where as modifing the default will give you a global update automatically.
Changing the default is what I recomend.
And you are using 08'? Im not sure how that works, my company went from inventor 7 to 2010. I should hope it would be similar.
Good luck. Just keep playin' with it

Thanks, I will.