Boric acid is dangerous to humans and animals when ingested (as are window cleaner, bowl cleaner, bleach, etc.).
When used for roaches, the usual method is to dust all corners and wall joints with a duster (a small vessel used specifically for acid dusting). This is generally safe as long as you avoid food preparation areas (which seems to defeat the purpose in the case of roaches), but can pose a problem to pets and/or small children, as they may ingest an unsafe amount.
I'd go for the organic safe option myself..
But if you insist:
Avoid consumer roach powders with boric acid in them; the boric acid powder is the active ingredient, so just get 100% boric acid powder (most dollar stores and home improvement centers have them, and it's generally cheaper).
If you DO have pets or small children, or the infestation is particularly plentiful, there is an alternative method to dusting... wall treatment. This is how it's done:
1). Mark off all studs in each room so that you know where they are (simple pencil mark will do).
2). Drill a small hole in the wall area between each stud, just big enough to insert the tip of the boric acid container (most brands come in a plastic bottle with an applicator tip) or the end of the duster.
NOTE: Avoid all air circulation ducts, pipes and wiring!
3). Deliver the boric acid powder into each hole (about 4 or 5 tablespoons worth seems to work just fine, but it depends on the roach population).
4). Spackle up the holes.
That's it!
It seems like a lot, but is really a small price to pay when you have a roach infestation... and it will keep away roaches (and a few other pest bugs) for about 8-10 years.
Boric acid powder sticks to the roaches, poisoning them and their eggs, following them everywhere they go and infecting (so to speak) every other roach they come in contact with. It kills just about everything within the first 24-48 hours, but you will generally SEE more roaches during this period, so expect it and don't worry... they will die.
Now the nasty part...
There will be bodies. The more you have, the more bodies there will be, and clean up can be disturbing.
Any substance that can kill something continually for the next 10 years I'm not sure I'd want anywhere near where I keep food and eat.