I was wondering if Morrowind without the expansion packs but somewhat modded works fine on my computer, then will Fable, The Lost Chapters work as well as Morrowind alone?

Best way to find out would be to tell us your computer's specs.

Me, I'd opt for the Morrowind expansions anyway because Morrowind is better.

Fable's easier on my computer than Morrowind is. The latter seems to be so poorly optimized -- it's much more taxing to run than it should be in my opinion.

I think that's an answer to your question. Then again, I'm not exactly sure what you asked.

Keep in mind that Morrowind, whenever outside, probably has more to render and process than Fable. Everything in Fable is split off into separate areas while Morrowind is one giant area (not including interiors).

(I say probably because Fable is more recent than Morrowind so that could throw things off a bit)