I will be having 3 1/4" wide 3/4" barzillian cherry installed where I currently have carpet and tile. The stairs are currently carpeted and the installer wants to put the hardwood strips and nosing over exhisting stairs. I think solid treads would look best. Is it possible to buy prefinished treads and risers and simply put them directly over exhisting stairs? Or would a whole new set of steps have to be built? Which is the best way to turn old steps into hardwood stairs?

Use the flooring, it will match the rest of your flooring.

The best way is to remove the existing and install all new solid treads and risers, to me they look 10 times better than using flooring with nosing's.

I believe they are available now in a prefinished but I'm not really sure. Check our host's main website for cost and availability.