While obviously well-intentioned, Zoetrope's advice isn't the way to go. The drawback is this: while it is cheaper to copyright all the songs as a "collection", the copyright office FILES the collection under one name: i.e. "Barrt's Songs". Great. Now I'm Mr. Producer looking for material for one of my artists, and I hear this song-( the one people want copies of at your gigs) - say it's called "I Love You Baby" - so I check BMI's and ASCAP's database - not there. I check with the copyright office - not there.
(It's THERE, but under the title "Barrt's Songs") Now I'm trying to decide if the song is copyrighted at all; if I think it's not, I will pass on the song. Why? Because reputable producers are deluged with material that IS properly documented, and won't touch a song that even appears unprotected. Lawyers.
I would suggest you do both. Copyright the CD as Zoetrope said, but get a seperate copyright on the potential "hit". Then try pitching it to people in the biz. Join BMI or ASCAP - (I'm in BMI so I'm biased) - they can really help you understand all of this, and if someone picks up the song they'll make sure you get paid.
As for "publishing"; technically, you have published the CD as soon as you distribute it or offer it for sale. This doesn't make you a publisher, just as recording your own CD doesn't make you a recording engineer. A publisher has a staff that coordinates legal, financial, distribution, secures foreign rights, demos and promotes, the list goes on.
Hope this helps.