Stand one of the planks in a corner of the room. Measure the plank and divide it into three, marking the two points on the plank. Drill holes completely through the plank and into the wall.
Lift the plank away from the wall and insert the rubber washer between the two. Replace the plank and use a pair of wood screws to affix the plank to the wall. Repeat this process with the planks in all the corners of the room.
Nail plasterboard between the planks, creating a second wall, 2 inches from the original wall. Start at the bottom and work up to waist height. Repeat this all the way around the room.
Drop panels of the rock wool into the "pocket" you have created between the plasterboard and the wall. Work all the way around the room, filling up the lower half with rock wool.
Lean the rock wool sheets against the upper half of the wall and nail plasterboard sheets over the top of them, holding them in position. Repeat this all the way around the room.
Place the monitor isolation mats underneath your monitors, raising them up off the table or stand and preventing them from transmitting vibrations throughout the room.