All items listed in the Shpfilter.txt file will not show up in the Editor.
If you want to see all items then just rename the shpfilter.txt to something other than shpfilter.txt, or delete the file.
To select certain items to be seen, either delete them from the shpfilter.txt file or change the items name.
The easiest way would be to just put a "/" in front of the item.
For example: If "109F4" is in the shpfilter.txt file, that item won't be seen in the editor. If you made it "/109F4" by putting the "/" in front of it, it will then be seen. It would be the same thing as deleting it.
The Shpfilter.txt file is found in your C:\Program Files\HTC\aheditor\terrains folder.
Heres a file that I put together that may be of some use.
http://accesswave.ca/~tscott/AH-stuff/AH-Editor&Stuff/Shpfilter/SFv208.exePokie