The mod I'm speaking about is called Animated Morrowind.

http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=8118

Considering I know it can be difficult to uninstall certain mods and before I make the decision to install it, i wonder if anyone knows if this mod will have any FPS-hit if any and how much circa?

i ran it with quite a few other mods on a weak sauce PC (1.8ghz Sempron 1.5gb ddr 128mb ati) with out much of a problem.

You should give Wrye Mash a try, it's made installing/uninstalling mods on the fly indcredibly easy.

And as for the FPS-hit, there shouldn't be any more of an FPS-hit than with similar mods that add NPC's, even less I would say because they shouldn't be having any special scripts running as far as I know.

Actually, that is wrong - there are special scripts added to the NPCs. It's made so that they don't start a fight with you with a broom or mug in their hands rather then a weapon or shield. Given the limitations of the game this is the best way to handle these custom animations. On the other hand, you really don't have to worry about a great FPS hit from this mod, since the number of NPCs added with it is rather small, maybe a dozen or two. As long as you don't use the Animated Morrowind Extended version with it, which adds much more NPCs, you shouldn't experience any kind of FPS hit.

With a good video card, Morrowind is mostly CPU-bound and bottlenecked by a single core.
You will notice a hit with the following mods that use scripting. I still think they are worth using.

Animated Morrowind
Animated Morrowind II
Animated Morrowind Expanded
Atmospheric Sound Effects
Better Music System
Starfire NPC Additions
Starfire over Telvannis
Morrowind Comes Alive

On the other hand, if your video card svcks, you have other problems and might not notice any impact from scripting.

Beware these mods, they are very old but still have a huge effect on fps:
The Wilderness Mod
Fireflies Invade Morrowind