Adding in a advanced "blur-like" special effect?

[Spartacus]

I wanted to find out if anyone has a good article on like anything relating to making a "blurry" effect you know like the effect you can see if you look over a fire burining its "blurry." I was thinking I could make it and then add it with the enigne, if anyone knows exactly where I could find any info/examples on this, or how exactly this is accomplished.