Autotune in garage band.....

Hey all,
I have a question about using autotune in garage band, i don;t really like using it but in some songs it just makes them sound better. soo my question is...
Is it possible in the 1 track that your recording, that you can have it pushing the note to do different keys. (EG. In the song "Im so Paid - Akon Ft Lil Wanye" Akons part is in F sharp and Lil wanyes part is in D Major, But when you change the key it changes the whole songs key)

Another thing, the autotune in garage band is quite bad, is there any other programs that work with mac that you could sugest?

thanks in advance

I found this on youtube which might help to at least get that sound you're looking for.

One way that you could bypass the differences in keys is to record one vocal part, add the fx, and then just bounce that single track down and add the new file to the existing project.

-SCR