Here's a photo of my "Stairmaster desk," which I've developed as a Stairmaster alternative to the [http://www.treadmill-desk.com/|Treadmill desk].
The idea of a treadmill desk stems from research done by [http://www.cspinet.org/nah/index.htm|Dr. James Levine] of the Mayo Clinic. Levine studies "non-exercise activity thermogenesis" (NEAT), which is medical lingo for "activities that aren't strenuous enough to be considered exercise but still burn calories." He finds, for example, that just walking at a casual pace burns about 100 more calories per hour than sitting. He's therefore worked with a company called Steelcase to design a "[http://www.steelcase.com/na/walkstation_products.aspx?f=30670|walkstation]" that consists of a treadmill attached to a desk, where people can walk at a slow pace throughout the workday.
The only problem is, the Walkstation costs about $4,000, so hacker ingenuity is stepping in to develop cheaper solutions. Jay Buster (see link above) added a desk surface to a used treadmill, using $49 in materials. I don't own a treadmill, and I'm not sure I have the space for one, but I do own a Stairmaster (which I bought used a few years ago via eBay). I wanted to see whether a Stairmaster desk would work as well as a treadmill desk.