The Tarantallegra spell makes the victim's legs dance like crazy, where as the Jelly-Legs Jinx makes the victim's legs wobble. So it is safe to say that the Taratallegra spell is a stronger version of the Jelly-Legs Jinx. Also, besides the fact that they involve the legs, I think They involve the legs' muscles. Both the Jelly-Legs Jinx and Tarantallegra make the victim lose control of their legs. If we had teh time actually, we could possibly go in-depth on how the spells affect the muscles, and everything else. But that would take a long time.

*Takes a breather...*

I would also like to add that the Jelly-legs Jinx should be renamed Jelly-Legs hex not jinx, while the Tarantallegra spell should be a jinx or maybe even a curse.... But that depends on teh casters, and everything....But that is my opinion.