The best way to do that is probably using Get Color from Layer, where the particles pick up their colour from the background image. By turning that on, and selecting Intense, you'll get brighter copies of pixels from the image you're using as a background. "Particles Get Color Up" from the July 2006 library should be a good starting point, but there are many others as well (Distorto and Watery in the April 2007 library)
Not sure exactly what you mean about the text. Do you want one word to break apart and form another? The closest thing pI has to paths are Forces, which are good for moving particles around in general, but aren't a very precise tool.
I would evapourate on particular word into a plume of smoke and it would settle to form a different word.
I don't think PI will do it as I'd need direct contol over the path of each particle instead of just the emitter.
However, I did recently discover the neatest effect.......
Using the get colour and transparency from layer, then increasing the number and size of the particles, it would form a cloud covering the whole word.
I then saved it as an avi and created the next title in the sequence, this time using the same size, position and number of particles as the end of the previous title, then reducing the relevant graphs to show the word, then increasing them again to create the came size cloud to cover the word and so on for each title.
I then put them all together in my video editor and used the flashback wipe inbetween clips and also placed video footage between each title. The footage would appear through the text first and then grow to fullscreen.
Probably badly explained and it wasn't what I wanted to do initially, but it looked so good, I completely changed the intro to the film to accomodate this and scrapped my original idea.
At the moment, the movie size is 5gb so won't link to it yet.
I'll cut that sequence out and compress it to a smaller file as it's unlike any intro I've seen.
I'm sure some of you guys would make a better job of what I've achieved and would like to see a more polished version to see how good it can look.