Im trying to fashion a basic tab header out of a custom ListHeader. I have two questions on this:
1) Is there a way to tell which list header column is currently selected, if any, out of all the columns? Would I be able to track this using the sort functionality (even though Im not interested in actually sorting anything)?
Yes, this is exactly the approach that you need to take.
2) ListHeader Images - how do I set my own custom ones? I.e. Hover and normal. I tried going down the same route as what I did for the pushbutton, but couldnt get it to work. Is the ListHeader made up of TLButton's under the hood?
Unfortunately not
The ListHeader is made up of ListHeaderSegment objects (more specifically TLListHeaderSegments for Taharez Look) which, at the moment anyway, do not derive from the button classes (even though this would have been an acceptable design choice).
There are currently only really two ways to change the appearance of this widget:
1) Edit the Taharez 'layout.tga' file - which will only offer limited scope (especially for this widget), and obviously will affect the 'real' list header.
2) Create your own derived widget types for the list header and segments...
Not that bad actually, read on 
The ListHeaderSegment derived class is very simple; just needs a constructor and two rendering methods (for normal and hover). The ListHeader itself has an (optionally) emtpy rendering method, and methods to create and return an object of the segment type, and finally a method to destroy a segment object (typically these two methods are only a single line). If you need the ability to modify the images used, then you'll need some supoort methods for that. Additionally you need the factory classes for the new derived widgets (cut & paste is your friend ). This probably all sounds like a lot of work but it's really not 
If you decide to take this approach, I'm willing to assist in virtually any way I can
I'll mention again that eventually I'll offer some classes which can read all the required imagery layout from an XML file, thus removing the need to code new classes for 95% of cases, but this will be a while yet...
