Here is the code for my fire, this fire effect is not to robust really, I need to do a little more work on it so I can have true volumetric fire, also I don't like the multi mesh approach I am using either so will probably play with the shader to get it to run on a single mesh. In short I am not happy with it yet, but I am posting it here so you can at least see what it does and it might give you some ideas of how to do your own. When I started out playing with this shader my knowledge of shaders was very limited, now I have a bit more experience I will more than likely improve on this, if I do I will post it her.
So, the code...
So using this class in my engine for the screen shot above I set it up like this.
I have also found a bug (one of many) the mesh you are applying this to needs to have a texture with it or you will get a flame like this
As you can see there are a few bits of code commented out, this is because I am still working on this class, so little time, so much to do.
Here is the shader (thanks again NVIDIA)
I suggest you don't use this code or shader as it is really not of much use in a 3D world. Once I have some spare time I will make this fully functional. I guess if nothing else you can have a play with the shader and learn from it...