I don't have a .Mac account, but certainly most web servers will accept a set of HTML pages and folders and display them correctly from the web. I have looked at what comes out of Photoshop when you ask it to create a gallery, and this is just what it is. I assume Lightroom does similar stuff.
You need to upload that to your Web server via FTP or any other working mechanism. The first page's files should have a file called index.html in it, if not you are still missing something. If it is there, and you can point your browser at it, it will display correctly. You shouldn't need any .Mac cleverness to make this happen... I hope.
That having been said, perhaps .mac accounts are different? Has anyone used their .Mac account to publish "home grown" vs. iWeb generated web pages?