Milkshape is an Shareware Programme which you can test for 30 days and then for 25 Euros or 25 $ you can register it.
http://www.swissquake.ch/chumbalum-soft/
You cannot create Animations or really complex Levelmeshes for Gothic but to build little Meshes like Swords or Vobs or just Levelparts for Gothic it is sufficient. There is a special Import and Export Plugin for the Gothic Meshes for Milkshape. In the Tutorials Section you can find a tutorial to create Models for Gothic with Milkshape, but for that you must know how you can create something. To learn the modelling with Milkshape there are good Tutorials on the following page:
http://www.pierre-kretschmer.de/index.php?option=com_wrapper&Itemid=29
Far general information and Tutorials for Milkshape are on other sites enough, but it would be better if you look for them your own
http://www.google.com/search?q=tutorials+milkshape
