when cutting cove you can get a miter box from many painting and decorating stores they are far better than a template. when cutting the gyproc (plaster) cove i use a cop saw set to 45 drg as for the internal corners of a room you only need 2 cuts. this may seem extreem but if the saw is sharp the finish is very good. when joining 2 lengths of cove cut them at an angle as well as this will help hide the join when it is filled and painted.
james, June 2006