Lower the Chairs
Rather than trying to raise the table, simply shorten the chairs. Mark the legs clearly at the point where you want to cut them. Cut each leg using a circular or hand saw, then sand the base of each leg when you are done.
Add Castors
Adding castors to a table automatically adds 1 or 2 inches to the height. It also gives the table the added benefit of mobility. Purchase castors at your local hardware store and follow the instructions for installation. They come in many different styles and colors.
Furniture Risers
Add small plastic blocks -- marketed as furniture risers -- to the base of your table. These are often used for beds, but work well for tables, too. If the legs are too thick, add pad feet or wooden finials. Wooden finials often already have a screw in place to attach to the table.