Hi Anna. Good question. Although both devices use the CO2 laser, they are very different in how they deliver the energy.
During CO2 resurfacing, skin tissue in the epidermis and dermis (upper and lower layer of skin) is vaporized by the heat generated during the treatment. This represents a controlled burn and thermal injury. The procedure is usually done under general anethesia and involves long recovery times between 2-4 weeks. It is also typically very effective in one treatment at getting rid of acne scars and wrinkles.
The goal of the Fraxel Repair is to try and replicate the results of the traditional CO2 with less downtime, but more procedures. We have never seen results for fractional resurfacing come close to traditional. The Fraxel (fractionated) technology splits one beam of light into many hundreds or thousands of smaller ones. In this way the injury created to the skin looks akin to plunging a comb through a piece of tin foil. There are many laser entry points but the general structure of the skin is intact.
Web reference: http://www.celibre.com/laserResurfacing.aspx