Some SEO questions....

Duplicate content:
I know google penalizes sites that have duplicate content does this mean duplicate content across many pages of the same site? What does duplicate content mean? i "include" my headers, footers, navbars and/or advertisements using PHP on all my website pages...surely this is the most literal meaning of "duplicate", but i'm sure that google rankings wont be affected by such seemingly duplicate content.

Domain name vs content:
If i have a website that ranks highly in google, and i change a lot of the content on it, will the fact that my domain name is highly ranked help preserve my pagerank?

Adwords:
Lets say i pay the pay-per-click. Does the traffic generated by the sponsored advertising count towards your natural search ranking whatsoever...or does it hurt it?

thanks,
Leon

Duplicate Content means like you put the same phrase on your page multiple times trying to get it as a keyword hit. You would be spamming if you put too many keywords per page. This is keyword spamming. Duplicate over multiple pages is fine. Think like a company tagline on everypage, it isn't considered spamming. Really duplicate headers and footers aren't an issue, since they usually don't contain much of the sites true content.

If you change a lot of content on it, it will majorly change your ranking. Your content is probably the biggest factor in ranking. I don't think there is a very strong link between domain name and content, except when your domain has a keyword in it for the most part.

For PPC, I'm not sure about if it helps your ranking. Found an article here (http://www.bloggingtips.com/2008/04/02/how-does-ppc-affect-seo/).

Here is a good article on SEO http://www.btbroadbandoffice.com/businesstoday/0,,5733877,00.html