As stated above, the install should be completely based on how comfortable you are with mechanical things. Its not the easiest thing to do, and it does require a special puller for the pulley and the tensioner tool. With the proper tools, start to finish, taking my time of corse, it was about 4 hours. That included repairing and modifying the belt tensioner.
That brings up another thing to consider. You may need some additional parts, and it is strongly recommended to replace the tensioner or at least install a tensioner stop. Many times the tensioner damper is in need of replacement as well.
I went with a 17% pulley. Its been on for about 2 years. It went on the car when it had about 130K miles and now it has over 150k miles. So far no problems that are related to the pulley install.