Fire

For a simple fire, just have the particles ascend to a point and fade as they go up. When the particle's attributes such as the fade and the height exceed your stipulated limits, then return them to the bottom with default attributes. You can get a little more complex by randomizing the points or having multiple points and randomizing a percent chance of a particle going to whichiver point.

I've made a simple one that is customizable and has the source code included in C/C++ Here under Matthew Shieh.

Hope that helps.

Just start them with some dark red, and little transparency, and make them become yellowish, and higher transparency, as they move up.
There's really no carved in stone formula, just try until you get the best results.

Xiachunyi, the demo program was extremely helpful. Thanks a bunch....