It is possible to buy a fancy workstation and treadmill combination; the last I checked it was being sold for $3500 - $4000. You can make your own much more cheaply just by putting a shelf across front of the treadmill to put the computer on, and a shelf for the keyboard.
Dr. James Levine with the Mayo Clinic was one of the first to publicize this idea, though it is intuitively obvious for people who use treadmills and spend a lot of time at the computer. He walks all day at a very slow pace, less than 1 mph. Walking at any speed does seem to help the metabolism to speed up a little and the brain -- at least my brain -- to focus better.
Walkstation by Steelcase
Walking at Work, with Dr. James Levine
