Search for Geep's Poser animation tutorials here in this forum. Search especially for anything pertaining to the "Graph Editor." You can create smooth motion using the Graph Editor within Poser - it is the key. You can then save those animations as animations (within your pose sets) or export them as home-made bvh files. In the meantime, you can freely download a bunch of free BVH files on the net (Little Dragon please help me here - I don't remember the URLS!). Wolf359 also has some for sale. I've never used them but I don't hesitate to recommend them based on what I've seen of his work.

Before they made me they broke the mold!
http://home.roadrunner.com/~kflach/