The Haflinger Dynastart does not provide much "spare" electricity, so really a winch should be run from it's own battery with maybe a split charger to provide a trickle charge to the winch battery when it is not being used.
A reasonable size battery should provide two or three sessions with the winch before battery voltage drops too low.
The simplest way of getting a winch on a Haflinger is to use one like these:- http://www.northerntool.com/shop/tools/product_200466652_200466652 (just to give you the picture). These are not fixed tot he vehicle so they can be used front or rear - Just use a D-ring like these:- https://www.etrailer.com/comparison.aspx?pc=47-3406&pc2=BC-902
Run suitable long heavy duty cable to the seperate winch battery with a quick connection like:- http://www.ceautoelectricsupply.com/vhcconnectors.html
That way you can position the winch where ever you need it in order to extract your Haflinger which a fixed front mounted winch might not do.
John