If animated flames is your goal, you will prolly fail... as you will have trouble making the flames look realistic, my advice would be to use a 3D program... infact you could prolly even put your text in the 3D program, it could look good...
Ive got a old animation which had flames in it (yes the whole thing is animated, this is just a single capture though):
those flames look good in low resolution, and they take less than 4 minutes to make (i know the example looks bad, i were just testing some random stuff, the latest version of that animation had some "fans" on the letters that are rotating above the fire, causing the fire to partly swirl around with the text...), with some simple adjustments you could make it look good
I believe i made those flame by a simple "light" layer, put some mist like thingy to it (i believe it was a water effect) added wind to the light, and it simply looks like fire when you change the colours on it etc... (note that it takes some time to render 3D)