i did a lot of research on this before my purchase, but the sales person threw them in for free, so i didn't get a chance to put them on myself... but i remember there should be three screws, two shorter ones on the side and one LONG screw in the middle, and it is this long one that keeps giving people trouble while installing, because it is kind of blocked (partially) by the rear wheel (hard to access)...
it sounds like that you will either need a special screw driver, or you may opt to take the rear wheel off... pre-drilling the rear mud guards might also be required...
a lot of discussions have been posted in this category, you might want to do some searching... good luck....