A few things.

First off I'd like to ask which is better to start out with the rythem like guitar or an instrument of some sort for a song or lyrics first? Next, I write poetry so I usually turn them whenever possible into a song but my one problem is I cannot finish the song or it just goes on forever. Is there something i can do to fix that like an outline? Another thing, whats a good way to make lyrics of your song go with your rythem and vice versa (sp). Thanks.
And sorry if I don't make any sense of what I am saying.

Do the melody, and then write lyrics to fit...

I'm rubbish at the actual lyrics, so what I tend to do with the band is put together the guitar part, and then hum over it like I imagine the vocal line being. Then it's over to someone with an idea about these things to fill that bit in....

I did an English Literature degree, and tried to do the same as you - write music to fit my poems - I could never get it to work either.... :confused:

I've rarely been able to come up with satisfying music without inspiration most of the time someone would give me a poem and it would light a fire under me. Sadly I can't stand my own lyrics it always comes across to me as bu(( sh!t. But every song I've ever been truly happy with came from from varied inspiration e.g. depression, joy, drugs, co-writers, co-writers on drugs what ever floats your boat. But persistance above all else will prevail.

You wouldn't even believe how many times this question has been asked. Basically "how do I write a song". The simple truth is there is no set way. Write the way that feels right for the song. There's no magical formula that anyone uses (that I know of). Just go with the flow "yo".

Peace.