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Mule Team Borax is God's gift to flea warriors everywhere. It is cheap,
effective, and safe. You don't want to use in your yard, however, and
you'll also want to keep it away from houseplants, pets, children, and
so on. (Be especially careful if you have fish.)
The way you use it is to simply apply it like you would carpet freshener. Then work it in with a broom and let it sit for at least 4 to 6 hours (we usually let it sit 8 hours or so. The longer you let it sit, the better it will work). When you just can't take it anymore (you'll see what I mean), vacuum like a madman. It is also a good idea to vacuum before you apply it too because that helps stimulate the fleas & larvae to move around a bit and that makes them more vulnerable to the borax.
We have applied it to carpets, mattresses, and all sorts of furniture with no ill effects and with no sign of anything being discolored or anything like that. If you are a high maintenance person prone to all sorts of troubles then either don't use it or test it on a small scale first. Just remember that although thousands of people have used it with no problems at all, you are using it at your own risk.
For more information about using it, check out the page about how to treat your house for fleas.