Usually this happens during the setup of Internet Explorer 8, when that first IE8 welcome screen appears when you installed it. Choosing the "default" options during that setup isn't always the best option for many.
So....Open Internet Explorer, then click on Tools-Manage Add-Ons. Once there, click on the "Search Providers" listing on the left side, search through the listings then eliminate or disable all but the one of your choice. Now, click on the "Toolbars and Extensions" section and find any toolbars that you may not want, highlight each one and disable or uninstall it. (Some can be uninstalled from the Control Panel as well.) And since you mentioned the "Yahoo! Search" box, you may also have the Yahoo toolbar installed. It may be causing part of the problem.. Simply opening the Yahoo page and using their search function is different from having the entire toolbar installed. The toolbar throws extra stuff at you.. Uninstalling it and testing the waters may enlighten you.
It's your choice.
Hope this helps.
I have an HP with Vista Home Premium and I just went from IE7 to IE8. My problem is with the Yahoo! Search box on the upper right corner of the page. With IE7 I would type in what I was looking for and if I repeated it often enough it would keep track of it for me. I would just type the first letter and everything beginning with that letter that I had searched for previously would show in a list. With IE8 I get all kinds of weird information and history that I don't want. Is there any way to set the Yahoo! Search so it will work like it did with IE7? I don't want all of this extra stuff, I just want to go there and click on what was saved for me in the IE7 list. Help will be greatly appreciated.