According to the articles I've seen on this song, "In The Garden Of Eden" was the original title of the song, but the singer was too drunk/high/whatever to sing it properly, so it came out "In-a-Godda-Da-Vida." It might also explain why the song is like 15 minutes long.

VH-1's Pop Up Videos features Doug Ingle stating that he couldn't sing the song, but it wasn't influenced by drugs or anything else and that the title is Latin for Garden of Eden. I have a hard time believing that though because in latin Garden is "hortus" and Eden is "paradisus".

The Simpsons also did it up as a church hymn with the lyrics "In the Garden of Eden". Bart slips it into the church service as a hymnal, it sounds excellent with an organ by the way. It is available on the Simpsons Songs In The Key Of Springfield CD.