I have the Canuck Motorsports springs, I LOVE the look dropped 1.6". I'm pretty sure there's a tech article on the springs somewhere but it's pretty easy.
lift the car, take off the wheel, loosen the shock tower nuts, remove the bottom shock bolt, wiggle the shock/spring assembly out, mark where the top boot sits in comparison to the bottom of the shock assembly(I took a yardstick and lined it up straight and marked it on 4 corners with duct tape).
Then once it's off compress the spring, loosen to boot, take the boot off, take out the spring, loosen the compressors, compress the new spring, slide it over, put the boot on(make sure you line it up or you'll be pissed once you have to recompress the spring), tighten the bolts(I picked up all new hardware just to do some work while i was down there), repeat 3 times.
Garbone is right, the fronts are much more work, I don't know what he's saying with the rears, they were EXTREMELY easy, took me about 30 minutes on each rear.
I would recommend the Canuck Motorsports if you want to have the slammed look, the Eibachs are more subtle but still look clean!