Pman, the idea is right, but the power disc sander is way overkill. I would take a full sheet of 120 grit paper, folded in fours, and run over the walls by hand. If you do as high as you can reach down to the baseboard you should be okay. You can do an average size room in fifteen to twenty minutes. Start in one corner and walk the room 360 doing as high and low as you can reach, then drop to the floor and do the same for the low work, save your knees and time with less up and down.