the lice program is very effective, but it takes dedication.
I agree the nitty gritty is good, but whatever you use it should have metal teeth.
I sit my children down to watch a film, wrap them in a towel, smother their hair in conditioner and carefully comb through, rinsing the comb in a jug of hot water to get the conditioner/lice into the water after each comb through.
With a good comb you will get the eggs and the lice. If the infestation is really bad comb through every day until there are no live lice in the jug, and then comb every three days until I get no eggs(nits). Keep doing the three day comb through for a couple of weeks.
Be as gentle as you can and keep the dc busy with a ds, snacks (things you can keep replenishing like popcorn can be good, so don't give them a whole packet just a few at a time) and drinks so you can be thorough.
I have combed through ds's hair three times and got nothing but the fourth sweep got the louse.
I think hedrin etc can work but the combing method (use conditioner or olive oil) done properly always works, catches stragglers and once you beat the infestation, do the condition comb weekly and tie the hair back in braids (every day) so there are no loose strands - to avoid re-infestation as much as possible.