At a quick glance, I would say that your problem could lie simply in the fact that you have too much code, specifically js, in your <head> element. While Google and others have worked around this issue, Yahoo is not so forgiving.
Your code indicates that your are using a CSS to handle the look/feel of your site, but then you have a ton of <style> in your code also; I would try to incorporate this into your CSS lightening your code and allowing the bots to get quickly to the meat of the matter - your content.
The same could be said for your tables. You code has 140+ validation errors, many of which are in your tables - try to use your CSS for your background and border colors.
There are some great code folks here at
WPW and at
Web TIP.
To help them help you, it might first help to see what you can correct yourself by looking at
W3C.
Good Luck and Happy Ranking!