Ok, owing the fact that you own an SL600, i think going to this site and spending around 30-50 bucks wont hurt for a complete detailed description on how to do it.
Dont get me wrong though, if you car was something that a lot of people have, i can probably give you my generic guide but you own an SL600, i havent worked on one but im quite certain replacing the bumper maybe more than meets the eye.
But in a nutshell, lets say im there in front of your car, i would check the center bumper area where the grill rests for plastic screws, owing irs a benz it might be covered with another plastic piece.
I would also check for plastic screws on the side of the fender well because the front bumper is connected there by plastic clips as well.
Also check the underside of the bumper where the enging splash shield is located.
Sorry i couldnt get much detail. If i was infront of your car i can apply my texcniques, since frankly, remiving bumpers is a no brainer for me. I rarely consult manuals for most of the cars i remove the front bumper with.