Using flash to light up a subject and create background blur while isolating the subject and stopping motion is very popular in something like mountain biking. This is done by using rearcurtain sync.
What you are talking about can be done with the normal flash, throughout the shutter speed the flash gives off light multiple times to expose the subject throughout the frame in different positions. There is a setting on the SB900 that allows multiple flashes but i dont know what it is. The exposure needs to be spot on tho, I have never tried this due to the fact i don't own a tripod!
But experiment and show us your results and how you did it, it will be interesting to see.
You need a tripod, and the right term, I believe, is stroboscopic flash. You can set the frequency (in Hz) and power of each flash. This allows you to open your shutter for an extended period while the action is being performed in front of your set up. The flash should be the main source of light, and each flash will freeze a certain step in the action, thus the strobing effect will give you your multiple shots of action within the same exposure/frame.