DE (diotemaceous earth) is fossilized little hard shelled algae. It's kind of abrasive like pumice and used in a variety of applications like pool filtering, liquid absorbent, cat litter, etc.
When I had carpet and had a bad flea problem, I tried everything. I went through I don't know how many vacuum bags, bombs (which I now HATE with a passion), sprays, flea dips, etc. I found what worked (though caused temporary discomfort on my part, but no more discomfort than I'd already experienced was to make sure my dogs were dosed with Frontline. For some reason, it killed the ones on them, then any new ones that jumped on them from around the house. It took about 3 week, then we were flea free.
If you're doing the vacuum method, don't forget to vacuum your baseboards, windowsills, curtains, basically any and all cracks and crevices in your house. Fleas love those areas.
Good luck! It can be a battle. Luckily, winter is coming on and they always seem to just disappear for me during that time.