What's the best way to make a raised bed?

Suzanne emailed to say:
"for the raised bed- whatever is free is always good, barring that, check out places like Home Depot for their prices. I originally wanted railroad ties (very pricey) and ended up with 2X12s that I cut to length. Best dimension for garden width is about 4'- something you can reach across and not have to walk inside of, once the garden is built. So depending on the length of the hell strip, you may have something like 4ft x 8 ft by 12 in. You'll still want to dig into the existing soil as much as possible, then fill the new bed with soil (either purchased or from elsewhere in your yard), and then amend the soil."

the pity is pouring in!

No one has very nice things to say about my garden site. Tree roots, marauding dogs, nosey neighbors, but I wanted a challenge, what can I say? Everyone so far is recommending a raised bed. What is the best way to go about building one?

THE BEST SEAT IN THE HOUSE!

I've looked all over my small, downtown lot, and this is the best site I could find. It certainly isn't ideal. There are some trees, there is not that much space, and there are, shall we say, privacy issues. But tell me what you think...
In order they are, a veiw north, a view east, and a view west.