If there is an equivalent, I haven't found it yet. While the site will be editable in any HTML editor, I've had extreme difficult working with the way iWeb creates HTML files. iWeb likes to take a more graphical approach to web design, using lots of images, layers, and div's, which the PC apps I've used don't deal with very well.
I think there are three options:
1. Scrap what you currently have and start again in a "more traditional" web editor (with similiar wysiwyg capabilites as iWeb) like Dreamweaver, Frontpage, Nvu
2. Buy a Mac and iWeb
3. Become a master at HTML and image editing
Unfortunately none of the three options are close to ideal. I've had to abandon several sites I made using iWeb because I couldn't edit (even the text) with other programs.
I work with a small NPO. One of the coordinators uses iWeb to maintain the website, because pretty much anybody can use it. Problem is that he's leaving and will be taking his Mac with so I need to find another prog that is friendly to all of us who are HTML illiterate. Preferably it would be free, but we're willing to pay.