Homeless:
I'm not a regular musician like a lot of the folks here, but I have read one thing over and over from different people in this thread; "When inspiration strikes, write it down as quick as you can. The music and lyrics are slippery things, they'll go back where they came from if you don't act fast"......and they are soooo right!
Mbo;
what you need is one of those note-taking portable little tape-recorders. The cheap ones are not high-fidelity, but will serve to bring the songs back to you later. I had one once when I delivered pizzas, and couldn't take my hands off of the wheel to write things down. I wore it out. (I still miss the thing, but it is not high priority for me....bills come first.)