Yes I do know. Basically when you publish to your FTP directly within iWeb it makes a folder for every site you have, then creates an index.html file to direct to the first site. Your problem may be that the url is pointing to a subfolder perhaps, or there is already an index.html file on the server that you just need to FTP in and delete then try to republish.
I recommend publishing to a folder anyway, then manually uploading it to your server. That way you can add some SEO meta-tags to your files before you upload. Plus if you don't want your site to be in a sub-folder you can just upload it to the root level. for example if you publish with iWeb your url becomes http://site.com/sitefolder/page.html and if you manually upload it to the root level you can avoid that middle site folder and your url become http://site.com/page.html.
Hope that helps.