The actual process of making a vampire turn into dust and explode is remarkably simple - once I had the technique down I could dust a vampire in about an hour.  It's almost a shame there aren't more than 7 dustings in this film...

First up, the shot with the vampire exploding was filmed with the camera locked into position, with the actor miming a look of shock before dropping down out of sight.  This gave us a clear shot of the empty background, and it's a simple matter to fade from the vampire to the empty background in any editing software.  I found that between 3 and 6 frames of fading was fine, depending on how slow the dusting was to be.

The edited shot was then imported into 3D Studio Max as the environment background.  Here's where it gets a bit more technical...

I identified three or four frames during the dusting process, and drew an outline around the vampire for each of those frames, using a closed line.  I then extruded that outline a fraction to make it solid and attached a particle array to it, with particles set to form over the entire surface starting and stopping on the same frame number.  I used 10,000 standard "tetra" particles for each of the emitters with a little motion-blur and a noisy brown texture applied.  Oh, and a gravity binding too, to make the particles fall towards the ground.

Then it's a case of hitting the "render" button and sitting back while the scene is generated.  Ok, so it's not as pretty to look at as the Buffy vampire dustings, but for a simple fan-film like this, it does the job just fine.  Add a nice sound-effect on the top (mine is a mixture of a backwards lion roar and a couple of other noises) and the illusion is complete.