How can I get signed to a record deal?

I'm 17, have been singing basically since birth (but seriously singing since I was 7), have been playing the piano for about 5 years, recently started guitar, am taking voice lessons, and am working on writing my own songs (I currently have about 3 or 4 that are half-finished and many lyrics that just need instrumental parts). Once I completely finish 3-5 songs, I plan to record a demo CD and then post the songs on Myspace and Youtube. It is my dream to get a record deal, so that my pion (music) can become my work. What can I do to get a record deal? Do I have to have an agent to get my demo sent to record companies, or can I do it on my own? I know a lot of record companies will not accept unsolicited materials. Any suggestions for how to make my dream a reality would be really appreciated. Thanks.