I spent the afternoon getting a new treadmill, for the purpose of making us a computer treadmill combination. Turned out, it was dirt easy.
We bought a ProForm Crosswalk 480. At slow speeds, it has a nice, quiet motor, and at Sears, it was only $500 or so. Initially, I was looking for a model that we could take the display off of, but the more I looked at this model of ProForm, the more I realized that we could just do away with the vertical bars entirely. The 480 has a cable that comes out the back of the unit, and the display (once removed from the upright stand) lays flat on a shelf (see the picture below), making it ideal for what we're doing.
We've had an Ikea computer desk for a year or more, and I forget the name of it, although I couldn't really find it on their website, so they may not make it any longer. From their current catalog, it looks a lot like the Fredrik line, as far as being adjustable, with the smaller shelves and all.
So the short of it is that we assembled the treadmill without the upright bars, connected the cable coming out of the treadmill to the display panel without threading it through the upright bar, and just put it on the lower shelf. We adjusted the height of the desktop to suit Wife (and although it's probably not optimal, 8-yr-old Daughter can use it without complaint, as seen below), and we're off and running. Or rather, walking.
Oh yeah, and since we don't need any features on the treadmill itself besides having it let you walk, we got away with a much cheaper model. Big win all the way around. Especially when you consider that a "properly made" model, (like the Steelcase Walkstation, for instance) costs 7-8 TIMES as much.