The major similarity between these two presidential elections is that their results were disputed.
In 1876, the election was disputed because there were conflicts over the results in four Southern states. In 2000, the results were disputed because there were conflicts over the result in one Southern state--Florida. Florida's vote was also in dispute in 1876. Coincidentally, in both cases, the design of the ballot was controversial. In 1876, there were Republican symbols printed on Democratic ballots, which led to some of the votes being disallowed. In 2000, the famous "butterfuly ballot" made it difficult to determine who a person was voting for in some counties in Florida.
This is where the similarity ends. In 1876, the dispute was settled by the House of Representatives. The House is believed to have settled it through the "Compromise of 1877" that ended Reconstruction. In 2000, the Supreme Court ended the dispute.