In an effort to gain control over my Ginormous Seedling collection, I double dug a garden bed Monday. I didn't have my camera crew handy ;) ...so more detailed pictures will be available after I dig the next bed.
To get started I gathered some containers to hold the first row of dirt:

Ideally you would want to use something like a tarp where you can just kind of move the soil over without turning it over and disturbing it too much. As you continue to move the top dirt left you will want to just move it over, not turn it over. I've actually been doing this step wrong for years. heh. But have still had decent results.

After you've removed the top layer on the first row, you then take a sturdy fork like tool to loosen the bottom layer. You then continue by shifting the top 6" of dirt onto the bottom 6" of dirt you just loosened. Loosen the next bottom row and repeat. Here's a shot of about halfway through. In the picture below you can see the fork like tool I used to turn the soil. John Jeavons recommends using a square shovel for moving the top layer; although I've been making do with my regular spade shovel.

Thinking that turning the top soil over was the correct method, I put a layer of mushroom on top so that it would get worked into the soil.
Once you have loosened the last bottom row. You take the dirt in the bucket and put it on top of the last bottom row.

Aaron is particularly good at smoothing out beds so I let him turn this pile of dirt into something more manageable:

I then added some more mushroom compost on top:

I really don't care to buy mushroom compost bagged, but we haven't ordered our truckload for the season. Also if you don't live in an area that delivers mushroom compost in bulk, you can get this kind bagged at lowes.
After putting some compost on top I planted my squash:

I actually started these from seed indoors, and it did not take long to harden them off. The big outer leaves got floppy easily but the inner leaves stayed perky. So I took the droopiness of the outer leaves with a grain of salt, hardened them off for two days and then put them in the ground. They seem to be doing just fine!
So this is just a glimpse of the double digging process. John Jeavon's "How to Grow More Vegetables" book has some great pictures and instructional text that explain the process in great detail.