I've managed to make a lot of progress with my mounted Vampire Lord. It is the same character that I made before, I just wanted a mounted version too.
You can find an earlier picture and explanation of the model pieces with http://beyestudio.blogspot.com/2010/07/vampire-counts-lord.html.
Since then, I have finished building up the cape with green stuff and I have successfully attached him to his base.
To create the cape, I cut out small strips of plasticard, glued them into place, and puttied over them with greenstuff. I took it slow and did the cloth in sections, waiting for one piece to dry before moving on to the next.
Here is a look at the entire model.
The inspiration for the placement of the horse and tree was Tim Burton's Sleepy Hollow. I suppose I wanted my army to have it's own gnarled tree that bleeds, contains human heads in it, and occasionally shoots out a horseman. Although my guy isn't headless and he could just be jumping off of the tree.
The next step will involve puttying roots around the tree to blend it into the base, I will also fill those holes in the tree with skulls.