If you are under Vista or Seven, it is imperative to install the Morrowind video game elsewhere than in “Program Files (x86), Programs, ProgramData”.
Thus personally as much I installed Morrowind in a new repertory called "Games" for example, in the root of the disc C. (example: C \ Games\Morrowind \)
Because with Vista and Seven there are problems of rights of files and virtualisation of files (and that even while being on the session administrator of OS).
:user:
That's a bit vague and unfair in regards to the situation. Personally, I almost always have my "production" copy installed to the default directory on Vista (Program Files) and have no problems at all. The reason for that is I have User Account Control disabled on my rig (though, I don't personally suggest just any random person doing that - more so in Seven than Vista, but either way) and that is where the issue seems to actually reside. If you do intend to leave UAC running (which I recommend for most people), then it would be best to install to a different directory.
@Tricksy Hobbits: You shouldn't need to uninstall and reinstall. In fact, as per the sticky post on this forum, you can setup multiple copies of the game on your system if you like. Just make the new "Games" directory as suggested, and then Copy and Paste (for a duplicate copy, otherwise Cut and Paste to just move) the Morrowind folder on over to the new location. You will want to make sure that any shortcuts to launch things are properly updated as well so you launch the right instance of the game each time - but nothing too terrible.
Hopefully that wasn't overly much