The best way to add animations for an existing set would be with Oinkerwinkle's MDL Animation Transfer program from his download site Oinkerwinkle Downloads. Once downloaded check out his informative Tutorial for what ails you Oinkerwinkle Animation Transfer Tutorial. The beauty of this is the models must be in MDL format (Grom and New Animation donor)so any modeling prog will do, just make sure to have all the details of the animation in hand (Proper name and.. well.. see the Tut )