It depends on your scanner.
For small ones that scan sufficiently fast enough, the camera tripod works well.
For larger scanners I'd recommend something more supportive, like what the others have already mentioned, or, if you're lugging it between positions, go for a lighter carbon-fiber Dutch Hill tripod. http://www.dutchhill.com/products/heavy ... d-usa.html
It's expensive, but so is your scanner.
It is lighter, which helps on your carrying shoulder, the thermal coefficient of expansion is 3.5x better than steel, so direct sunlight isn't a problem and it is 3.5x stiffer than wood, so heavy weight is no problem.
Whatever you do, please don't use an aluminum tripod... especially in direct sunlight.