Those topics in ar15.com provide a good starting point. The freefloat handguard they show are the "traditional" types that require removal of the barrel to install the mounting bracket for the rear of the tube. Being a complete tube, the front sight has to come off, too, to allow the tube to be slipped on.
The newer free-float tubes come in two parts. The top part of the tube runs from about the 7 o'clock to 5 o'clock position, as viewed from the rear. It's held on by a substantion u-bolt clamp across the barrel extension. The bottom part of the tube then screws on to the top. You can leave off the bottom part if you're going to put a grenade launcher under the bottom of the barrel.
Because it's not a one-piece tube, the front sight does not need to be removed to install it. Also, more importantly, you don't need to remove the barrel just to put in a new barrel extension (or "barrel nut"), just cut off the existing delta ring, wave spring, and snap ring (the upper items in the following picture). The barrel itself is not removed.
I wrapped some duct tape around the barrel and upper receiver to protect against any nicks while cutting off the aluminum delta ring with a cutoff tool in a Foredom grinder. It was about a 10 minute job to cut two grooves deep enough to snap apart the ring with a large screwdriver stuck in the cuts.
I was much more confident in just cutting off the delta ring, and removing the spring and snap ring than removing the entire barrel. I did remove the front sight because I installed a fold-down front sight at the same time, and that let me get the gas tube out of the way. But with care, the front sight and gas tube can remain on.
I'll post a picture with more details of the new hand guard later.