There's no evidence that MSM can do any miracle to your hair but anyway powder is better than pill because pill has a lot more crap in it (magnesium stearate, cheap soybean oil, etc)
yeah i know it's not going to grow a forest of hair but i guess it can do no harm but help. i heard MSM is as non toxic to the body as water.. i ended up buying the NOW MSM caps since it seems to be easier to swallow a pill than taking spoonfuls of powder. it's only $6 bucks for a bottle of 120caps so i picked up a couple bottles for $13 and should last me 4-5 months.
(btw they great place to buy from and are the cheapest prices compared to all the other supplement sites. great shipping rates too.. my second order with them and they have tons of stuff!)