Hello I'm lookign for .X files animated and static models to experiment and use in demos. Any good site? The polycount.com is a very good one but how can I convert the game-specific formats into .X with full animation information? Thanks.

You can take any mesh and export it as .x.

Animated meshes are not easy to find... there are less painful ways of doing them (such as linking together mocap in 3ds, but you still have to bind a character). But animating is harder/less common than models.

Actually, as far as art goes, animating wtih .x is the same as any other format (programming is a different story). It is good because everything is self-contained, model, bone, animation info is in one package. For those same reasons it is a poor choice for a complete game. In order to modify one thing you have to modify everything.