How to add header to Wordpress & Pages or Posts for Serps?

I have 2 questions

1) how do i add my own Header JPG to the default Wordpress Theme?

2) if using keywords to get good search engine positions does it make any difference if i put 20 articles on 20 different pages or put 20 articles on 1 page?

 

1: If you dont know - use http://www.yvoschaap.com/wpthemegen/
2: Depends. Pros and cons for both... do what you feel makes your site the most userfriendly.

 

Thanks the WP gen worked great