Regarding Hugo's comments on why musicians study music and not lyrics, I think there is a bit of a difference.
The study of music theory (at least, Western music), will tell you about diatonic harmony, chord progressions, secondary dominants, borrowed chords, etc. In other words, it will tell you the "rules" of music. Of course, the rules can be (and are) broken all the time, but ... generally, it tells you what's proven to work and why it does.
In my opinion, music theory is to music what grammar is to english.
While the majority of fairly educated non-musicians aren't going to know music theory, most fairly educated people are going to have a decent grip on basic grammar.
So, if you want to write music, it will faciliate the process if you learn the "grammar" of music (music theory). Of course, many, many people have done it without knowing.
But the problem I see with teaching how to write lyrics is that lyrics are soooooo subjective. I'm not going to read a book on how to write lyrics if I don't like the lyrics the author writes. Why would I?
It's easy to say the diatonic triads in C major are C, Dm, Em, F, G, Am, and Bdim. That's a fact. It's also easy to diagram a sentence and say what's the verb and subject, etc. Those things are facts as well. But who can say what "good" lyrics are? It's very subjective.
I'm not saying that it's a total waste of time. But I've read several books on songwriting and/or lyric writing, and I can say that I've learned more by studying the works of songwriters that I like.
For my two-cent suggestion on helping to write lyrics, I'd say this: Do lots and lots of freewriting. Do it every day when you wake up or before you go to bed. Write several pages of whatever comes to your mind. Don't try to make sense out of it. This will help (or atleast it helps me) train you to channel your subconcious creative side. I know that sounds a little cheesy, but it works for me.
Anyway, sorry for the diatribe.
