We're in the process of building a vegetable garden in an area that was covered in thick ivy for decades. Our plan is to include two raised beds that we'll make ourselves.
I read a brief piece in the West County Times on Saturday about the potential problems with using treated wood for their construction. Some studies have shown that chemicals used in the treating process can leach from the wood into the soil. Alternatives include untreated cedar or redwood (which rot less quickly), stone, concrete block or brick.
Good instructions on building beds can be found on Sunset Magazine's website.