Quick ? about duplicate content.

I have a nice 500 word sales page that I'd like to rank for 5 or 6 keywords.

I understand it's best to make individual pages for each keyword and title each page to match the keyword.

Could I get high rankings by making 6 individual pages, then writing a 300 page unique article at the top of the page, then depositing the same 500 word sales pitch at the bottom? Or would Google penalize each page for having the same 500 word sales pitch?

Not good. Why not have an article page and then direct each of the articles to your main sales page.

I see. That's what I'll do then!

Google doesn't penalize for duplicate content. They simply don't rank it high. So I guess you could call that a penalty. I would just make 5-10 500 word articles for each keyword, have a link to them at the bottom, and then make sure those articles are linking back to your sales pages (and possibly to each other).