Ask Mr. Smarty Plants

"To remove tannic acid, you must leach the acorns with water.  The Indians set the acorns in a basket in a clean fast-flowing stream.  The water rushing through the basket would leach out the tannins in a day or two.  Since most of us do not have a clean fast-flowing stream nearby, we need to boil out the tannins....Toss the nuts into a large pot, and cover them with plenty of water.  Bring to a boil, then boil for about 15 minutes.  The water will turn brown, the color of tea, as the tannic acid is extracted from the kernels.  Throw out the water...and replace it with fresh water.  To save time, have a second pot of water already boiling.  Reboil  the acorns, throwing out the brown water, several times until the water no longer turns brown."

Lee Allen Peterson in Field Guide to Edible Wild Plants: Eastern and Central North America says:

"Whole kernels, stripped of their shells and boiled in repeated changes of water until the water no longer turns brown, can be roasted and eaten as nuts or dipped in sugar syrup and eaten as candy.  Dried and crushed acorns can be placed in porous bags and put through same boiling proces to remove the tannin."

Euell Gibbons in Stalking the Wild Asparagus also recommends boiling in several changes of water for a period of two hours to remove the tannins.  

With the same recommendation from three people who know their wild foods, I think I would give the boiling method a try.  You should be able to tell if it's working by the color of the water coming off the boiling.