Hi,
I have written an article on the first steps required for WordPress SEO. Check it out here:
http://seo.blorc.com/seo/wordpress-seo-first-steps/
There’s a plugin called Tags in the Head which can do what you’re asking:
http://www.maxpower.ca/wordpress-plugin-tags-in-the-head/2006/04/17/
I have written something for this, so hopefully you’ll find it useful:
http://seo.blorc.com/seo/tagging-meta-keywords/
