If you login to the business pages of your Yahoo account you will see a section called, "file manager", that is where you're files are housed in Yahoo Sitebuilder. They don't really have a control panel like you are talking about. But you can move your files to an FTP if that helps.
There's a plugin for cPanel called RvSiteBuilder (I think that's what the name was) that works much better than Yahoo's sitebuilder (in my humble opinion). If you didn't have it installed when you signed up, I think you can get it for just a small monthly fee.