Do you need to keep the original Desiderata Valley for some reason?
If not, this should work as it does to reset any other Maxis neighborhood, but I haven't tried it yet with FT. Go to your My Documents\EA Games\The Sims 2\Neighborhoods and delete F001. Then
*copy* the F001 from your Program Files\EA GAMES\The Sims 2 FreeTime\TSData\Res\UserData\
Neighborhoods.(*Not* NeighborhoodTemplates)
The F001 in NeighborhoodTemplates is the default the game uses to provide Desiderata Valley, you don't need to use that one. The one in the Program Files\rest of the file path above\Neighbohoods folder has the playable neighborhood. If your templates are in, I don't use them so I'm not sure, will resetting it like that be enough to make the sims acceptable to you?
Another way would be to rename your My Documents/EA Games folder and restart the game. That will give you a fresh copy of all neighborhoods. You could again delete the Desiderata in your game and replace it with the F001 from this new game. This last way keeps the neighborhood story, I don't know for sure but I've been told copying the neighborhood from Program files loses the story...
if that's important to you.
Then delete the new EA games folder and rename yours back to say EA Games.
Otherwise if
you do need the original F001 kept there, any replacement for it to make it the third neighborhood has to be completely renamed, the F001 folder itself and
every other folder or file inside that that has F001 in it's name has to carry the number you want it known by. If every file is not renumbered correctly the neighborhood will not show up in the menu, I use this program to rename/number neighborhoods.
http://www.antp.be/software/renamer My current hood is named F1 and when I tried installing it as hood 3, the game would not let me install the original valley terrain with Sims and houses It said I could only install the Sims.
I'm not clear on what you mean there, unless it said that because you had copied the F001 from the wrong place.
Please note: The original neighborhood folder you no longer want
has to be deleted before replacing it from the My Documents part of your game, not from the Program files. If you try to overwrite it that can lose sims and/or lots and cause problems. And you need to copy folders from Program files, the game needs the originals kept there.