Whenever I had bathed the cats because of fleas I've just used regular (good quality) pet shampoo, basically soaking the cat in water combined with any (non-harmful to the cats) soap will kill the adult fleas on the cats. Dawn is apparently safe to use - that's what is used on birds in oil spills etc.
I don't have any experience w/diatomaceous earth
The vacuuming of carpets etc doesn't necessarily need to be professional strength, just frequent while you have a flea issue, the eggs/larvae aren't super sticky to carpeting etc so a regular vacuum works.
