As per my reply on phpfreaks...
1. It really depends. Ask yourself if you feel your project will benefit from a framework or if you should use something like a CMS instead. Realize that existing frameworks are worked on and tested by thousands of people, so there is generally high quality code, performance, and security. Can you deliver the same end product?
2. CodeIgniter is very easy to pick up, and is a pretty decent framework so I would start with that.
It is always fun to make your own framework though. Not necessarily for a production website, but just to learn how everything works.