As long as you can transfer the model type to .mdl or something else MED recognizes you can skin, animate and alter the models however you want. Although the models you can buy on the internet varry by if they have a skin, or are animated and if they are in a foreign type that can't be translated into something MED can use (highly unlikely, if not impossible with the right tools) there is still a good chance you can use what they give you in WED, (don't quote me on that WED part though)