1997 Toyota 4 Runner SR5 rear brakes are squeaking

1997 Toyota 4 Runner SR5 mileage: 143,000. My rear brakes are squeaking and I am assuming that the pads just need changing. A shop in the area quoted me over $100.00 for the repair, but the parts should only cost me about $40.00 to $50.00 at a local auto parts store. I would like to repair them at home, but am a little worried because my vehicle is a 4WD vehicle. Does this make any difference when replacing the brake pads? Are there any specific things I should look for when doing this repair? Any help is appreciated!