maby simplier then i think.
It is quite simple actually, if it bothers you so much that you'd rather have Vanilla, going into Textures folder and deleting all the texture files is all you have to do (if you don't have much (or at all) other mods. If you have a lots of mods then it can get problematic since I assume you don't know what texture does what and that you don't have any kits for viewing them.
Personally I suggest downloading everything by Connary from http://mw.modhistory.com/search, that's the best you'll find that's closest to vanilla for architecture and flora/ground texture. And it keeps the dark feeling of original game very well. On top of that I personally much prefer AnOldFriend's textures, so after I apply all that I want from Connary, I put http://morrowind.nexusmods.com/users/31611 on top. For weapons, armors and shields you can grab http://planetelderscrolls.gamespy.com/View.php?view=User.EntriesListing&id=119915, they make mentioned things look a lot more high res.
Fastest and easiest way is a clean, separate install. Rename your current Bethesda Softworks folder to something like "gamesasTextBad", then re-install Morrowind, and place whatever textures you want into the new install.
Wtf, why would he do that? A whole new installation just because a couple of textures are not to his liking is overly radical for such a minor problem.