for the effect of "fire" (the prism effect) carrara has the ability, but not "out of the box" so to speak. if someone programs a plugin to do this in 1 step, and change refraction values and calculate more beams of light, then it'll be easier, but until then, to get the effect that is most realistically what happens, is make multiple renders. 

remember the lighting you used, and refraction values, then turn off all light values except for red, (ie you have 3 lights, RGB 255/200/200, change to 255/0/0 ) and render.

then switch to green channel of your lightiing, and change refraction just a bit (forgot exact values, you can play with a straight 3 sided prism and 1 light to see these effects) and render. then do this step for blue channel as well.

put the 3 color channel renders together in some paint program, and you're done.

if you want more exact pictures, split the color changes a bit and use red, yellow, green, cyan, blue, violet, or even more if you want to put the time into it, and understand how to add layers together.
 
this is one of the main reasons i moved to carrara in the first place, you can do it in poser, but no direct way for getting caustics. poser can fake caustics i'm sure if someone spends months to find how, but carrara is more direct. and be aware that if your material is a perfect red, or perfect green, that it get rid of the rainbow, but there are multiple shades of red in the world, so the idea still applies.