a compact crank is a crank that has smaller rings (usually a 50/34 or 35 compared to the usual 53/39). this allows you to achieve lower gearing that is comprable to a triple without sacrificing shifting quality or weight (although this isn't a major concern). going to a compact is defidently cheaper than switching to a triple. Check out the FSA line if you decide to go that direction. I don't think you need to worry about your pedals, but you may want to use the cleats that allow for float. Look style pedals come with two types of cleats (you may haave to buy the second type seperately). the first locks your foot into place and does not allow you to rotate your foot any while you are clipped in. The second type allows you to rotate your foot a certain amount (with look, i think it is 6 or 9 degrees) while you are clipped in. This rotation is called float. having several degrees of float can help to spare your knees. You may already have the float cleats, but you still need to make sure that they are positioned properly on the shoes. You may also want to consider spending the money on a professional fit, this can help a huge deal with knee issues and they can further advise you on shoes/pedals/float based on your body mechanics.