Ok, let's see if I can take this one at a time. Yes, there is a special tool called a fore end wrench designed to remove that nut. Brownelle's sells about 40 different kinds for around $20. The nut is not held on with Loctite as far as I could tell, but it doesn't spin off easily either. After the nut is removed, the fore end slides off fairly easily.
Here's what I did to remove mine (and beware, it's redneck, get the right tool for the job, buyer beware, ymmv, etc.). I took a smallish pair of needle nose pliers and spread them apart so that the each of the jaws fit into one of the slots on the nut. Then I carefully turned the pliers to loosen the nut. You kind of have to be careful when turning because the pliers can close up on you pretty easily and will pinch the shit out of you (or gouge, stab, cut, puncture, scrath, etc.) Same thing in reverse for tightening when replacing the fore end. I told you it was redneck, but it works well enough and saves you the $20.