hmm, very helpful helpfulguy....erm...maybe not!
The way to tell if it is flea dirt is to get a piece of white kitchen roll make it damp and then put some of the little crumbly black bits on it...if after a few minutes you have a dark reddish circle on the tissue then it is likely to be flea dirt. As they drink the blood of your kitties and so their faecal matter will also be bloody. As for the little white things...they could be ticks I guess try and see if they have minute little legs at one end of their body.
If it is fleas then head sown to your vets sharpish and pick up dome frontline for cats, its brilliant, it kills fleas, ticks, ear mites and I believe now it is killing the flea eggs and larvae too, so your house should be fine.