http://cg.tutsplus.com/tutorials/blender/introduction-to-smokefire-simulation-in-blender-2-5-day-3/

In this invaluable, in-depth series we’ll be taking a look at smoke and fire simulation techniques within Blender 2.5, and who better to take us through this process than the man behind the official documents himself, Gottfried Hofmann. In the 3rd part of the series we continue to prepare the hi-res setup, and we also look at tips on saving baking time and how to keep the simulation stable. Prepare to be amazed at just what Blender can do for free!