Never heard that yahoo uses page rank system. I use yahoo search engines too, especially to search China websites. One thing about Yahoo is that it accepts duplicate content, and chinese are notorious for plagarism. So when I search for little known historical persons, all the top 20 results display the same article. It's hard to know who is the original writer.
You can blog and do article marketing. It's free. I know it's time consuming, but the more you write using relevant keywords, the more traffic and ranking you will get.
I believe it calls in different name rather than pagerank its call webrank for yahoo. Here's a site to where you can check it. I just encounter this today. ^_^
No functionalists for page rankings in Yahoo, only provides google, if you need then download google toolbar.