Pull up atlatl on the web, check the Primitve section here.  They come in several styles.  Basically, get a strong stick or board about 2 feet or so, put an antler or bone point in one end and get a dart with a depression in the butt and throw.  Have fun!  Also some kits available.  Helps to have a dart rest on the grip area, if you want one.
Hawkdancer