Like Jonathn Hobbs mentioned, some of your questions have been answered.
As far as finding an artist to collaborate with as a beginner, here are a few tips:
Nobody knows you are a beginner, you are only as good as your current project.
Unless you have colleagues you worked with in the past, no one knows your level of skill.
What matters is your current game project, some artists will not want to work on certain game projects regardless of your skill level, you could be John Carmack and still some people would refuse to work on certain game projects, especially when there is no funding involved and they are devoting their time and energy freely.
Sometimes all it takes is a beginner to write an interesting and fun game. Programming skills do not equate game 'funness' levels. You can be a great programmer and no good game maker if you simply don't have a knack for it. Relying heavily on testers could help, sometimes it is not enough.
My best advice would be to start making a game with no graphics, use 'programmer art' instead of relying on an artist. Programmer art is placeholder graphics used while you are still concentrating your energy on gameplay, game logic and bug fixes.
After the game is playable, if it is any good, a lot of people would be glad to help, some skilled beginners might help for a symbolic fee of 10$ or so, or for free.
If the game is not good, concentrate on making it good, who cares about art, gameplay is your responsibility as a game designer and it should come first in your mind.
Once it is good, it does not matter if you are a professor of Computer Science or a seven year old using some free game developer tools, people would be interested in helping with art and sound.
You also asked where you could find a composer, well there is a large database of music in http://www.newgrounds.com and you can ask the artists there for help with music, some of them are offering it freely.
You can make placeholder sounds at first using bfxr or sfxr.