For small pieces, I suggest boiling the wood in a pot of water on the stove. That will kill most bacteria, fungus, microorganisms, etc. as well as leach out the tannins and lignins which will turn the water brown. You may need to do it twice. If the wood is too large to boil, you can soak it in saltwater in a trash can. You can just add pond salt or aquarium salt. The salt helps disinfect it some. At the very least, you want to soak the wood in water in some container for a few weeks, changing the water as it browns up. There's a risk of adding something to your aquarium with the wood if it's untreated. That's not to say that things will go wrong but keep it in mind. Another problem with driftwood is that it may float depending on how old it is. You can anchor it down with something.
Also, see http://www.fishpondinfo.com/plants/decor2.htm#drift