You can get stuff called fibreboard in builders merchants. Not sure what it is supposed to be used for but I got some about three or four years ago to make some very big notice boards.
It is quite lightweight, soft and fibrous in 8' x 4' sheets - you have to handle it gently or it will get broken. I made a recessed frame by surrounding it with a strip of 2x1 planed timber (which is the same depth as the board) and then a strip of slightly wider timber moulding glued and screwed on top to hold it in place. (Put up a base and side strip of 2x1, hold the panel in place and put up the top strip which will just hold it enough to finish the job). Then painted the whole thing with a couple of coats of emulsion which held the surface of the board together. It has been in use since and is fine.
Only thing is that you have to use pins to hold the pictures in place, which you might not want to do with the children around.
Or buy a sheet of thin ply (you would get an 8x4 sheet of thin ply under €10) screw that into place and paint it with gloss paint so that sellotape and bluetack come off easily. Use washers on top of the ply when screwing it to the wall, 6 screws should be enough and the holes will be easily filled when it is all finished with.
Last edited by looksee; 04-03-2012 at 17:55.