You could just use the alpha channel object to achieve transparency effects and then write your own physics engine. If you ask me, it's a lot easier than dicking around with the particle extension, and it gives you a lot more control.
the hard part in that is devising a formula for it, that's where people give up, since they're too lazy to even bother with math, that's where the wannabe's are seperated from the pros
well, math wise, I suck, so i'm looking for an easy solution.
I've actually had great results with the particle extension, it's just a shame that it only allows one generator.
as for that seprating the "wannabe's from the pro's" I'm actually a professional graphics artist and game designer using MMF to test my concepts, so I don't want to spend weeks doing something i'm not skilled at to get something working.