There has been some good tuts about mountains but I would also suggest just stealing real earth mountains for your map. You can get height maps, contours or other types from the web. Nasa images are usually public domain so generally they are safe to use.

Have a search for Pasis tutorial which I recall did some good mountains as part of it. Also with PS7, I would check out the preferences or options. Usually, apps have an undo limit or a RAM limit set aside for undo. Its normally more than 1.