Edit: Tried it and it didn't work
.
Sometimes it doesn't. Don't know why. There's another way to add them manually, but it takes a bit more time:
Load up the Ayleid Ruins Tileset in the CS as described in my last post.
Right click in the list of pieces and select
New.
In the window that opens, click on the
Add NIF File button and another window will open, this time to your Oblivion/Data folder.
Open the folder named
meshes, then the folder named
dungeons, then the folder named
ayleidruins, then the folder named
iterior and double click the piece you want to add.
Unfortunately, you will have to do this for each piece you want to add.