Shattered Kingdoms

do you get a chance to improve with every line of the song?

Yes, and on every off-key note, and on the beginning of each singing check.

EDIT: You need every single one of those checks. Mastering some of the higher level songs takes a long, long time.

So actually, in order to improve a song, you need to start/stop singing it over and over?

No, you don't need to start/stop over and over again.

The help files state that you can learn other lyrics from other bard through the teach command. Does that mean you can teach more then just j-man and down or is that all of the songs?

And is there any difference in the songs of protection? Are certain lyrics more powerful?

Lyrics are unlike other skills. They can be taught all the way up to the highest level songs. The songs themselves cannot, however, be taught above j-man as usual with skills/spells.

No, the different lyrics do not change the effect of the song. They are purely for variety.

And you also still can't teach lyrics to other bards until you are at least a mentor level bard.

I didn't think that needed to be stated, but just in case that wasn't obvious, the other caveat to teaching lyrics is that both bards need to know the song in question superbly.

Well, I thought it important to mention because if you're training with another bard at lower levels and you both learn different lyrics to the same song (likely) then you can't sing in harmony unless you either level up, or find a higher level bard who can teach you both the same song.

Not that the issue should ever come up... but it's still interesting.