Draw a line on the subfloor. Mark between the straight walls and adjacent to the planned curved wall at the end of the walls nearest the curved wall. For instance, when creating a curved corner, the line would be on the diagonal between the corner walls.
Measure the line with a measuring tape. Cut a length of string equal to half that measurement plus 2 inches. Tie one end of the string around a pencil. Drive a nail partway into a wood subfloor at the midpoint of the line you drew in Step 1 and tie the opposite end around the string.
Pull the pencil end of the string taut. Trace a curved line on the floor beginning at the outside edge of the end of one straight wall and moving across to the other. Measure the length of the line with a measuring tape.
Cut two pieces of flexible track to length with a hack saw.
Line up the outside edge of both pieces of flexible track along the line you drew on the floor in Step 3. Curve the track by bending it along the pivot points between the steel plates in the tracks.
Hammer down the small tabs along the pivot points all along each piece of track. This locks the curve in place. Set the second piece of track aside.
Screw the bottom track along the line on a plywood subfloor. Use drywall screws and the appropriate screwdriver through the predrilled holes in the track.
Slide a 2-by-4 that's cut about 1 inch shorter than the ceiling height into the track on one end of the curve. Turn it so the 1 1/2-inch edges of the 2-by-4 are against the raised edges of the track.
Screw through the raised edges into the stud on both sides. Attach another stud in the same manner at the center of the curve and at the other end.
Slip the upper track in over the three studs, but do not affix it to the ceiling.
Insert additional studs into the tracks every 8 to 12 inches depending on the degree of the curve; the tighter the curve, the closer together the studs. Fasten the studs to the tracks at the bottom with drywall screws.
Check that each stud is plumb with a spirit level. Make any necessary adjustments to the upper track and affix it to the ceiling with drywall screws. Affix each stud to the track on both sides with drywall screws.