How can i up my web page in yahoo ?
 

My website is appear top 20 in google on web design company keyword.

when i search in yahoo.com with same keyword my site is not appear in top 100.

That is because Google and Yahoo use different ranking algorithms and no wonder some changes are observed in your web stats. Of course it has been suggested by experts that through using a standard and strong optimization campaign, rankings of websites on all major search engines will gradually improve. Yahoo usually is believed to favor on-page elements more than Google. So creating some keyword-rich pages can be one option. Anchor texts of the incoming links too can greatly affect Yahoo positions.

Forum posting is good for SEO purpose and it is a steady and slow process to get good links