Yahoo is very similar to google, in their SERP ranking. They rely on a variety of different factors to determine the rank of the page. The most important seem to be title, H1, H2, etc... tags, bold tags and keyword density. Also, probably the single most important for any search engine is good anchor text links.
Yahoo
PR isn't released yet, so I really dont know what it is based on, but if it is like google, it will be based only on inbound links.
Yahoo crawles about every day, if you have good links into your site.
In my experience if you try to optimize your site for google, and work on getting good high quality anchor text links into your site, you should rank well in yahoo too.