i guess there are a lot of different ways to simulate fire.
For example pixelmanipulation or particles.
What are you looking for and what do you need it for ?

Here is one of the better Processing sketches by Peter Blaškovič that captures "drawing fire"

Peter Blaškovič

http://www.escapemotions.com/experiments/fluid_fire_3/index.html

You can also check out his other awesome sketches

http://www.escapemotions.com/experiments.html

hey Cedric,
I'm working on an installation in a church (for Nuit Blanche) using PIR motion sensors to sense when someone is walking down the isle of the church.  There will be projections along the ceiling, above the pews, so when someone hits the different points along the aisle,  "fire" will draw itself (or maybe shoot) across the ceiling of the church.

something like that.

I want to see how other people have expressed fire in processing.  This Blaškovič one is fantastic, and I would love to create something that looks like this.  However I'm looking for some starter code, since I havent attempted anything as ambitious as fire in Processing before.

no code, but this one just came to my mind.
http://vimeo.com/3047446

that's fantastic, and entirely appropriate to another installation I'm developing tracking a dancer's body and creating a silhouette of fire.  Once I get the fire thing down, that is ;)