Whatever gave you the idea that you can't use the iWeb blog any longer? Of course you can still use it, however, the comments will not work on it because comments were always MobileMe only, so if you publish your website to another host/server, then you have to find a workaround for the comments.
There are a couple of possibilities here - you can use the commenting system Disqus or IntenseDebate which is free and can be found here - http://www.intensedebate.com. This is easy to set up and will allow comments to be left.
You can use WordPress as your blog if you wish to and Wordpress.com is free as opposed to the Wordpress.org which is installed directly on your host/server.
If you use Wordpress, then you do not need to fiddle around with html snippets in iWeb at all. All you do is go and create your blog at Wordpress and then in iWeb create an external page link to your blog and that is it. So you would have a main link in iWeb that says something like 'Blog' or 'My Blog' and you then create an external page link via the Inspector and hyperlink and when someone clicks on the link 'Blog', they will be taken to your Wordpress blog.
If you really want to use an html snippet, then you can do, but all you would do is display the blog directly in iWeb as an iFrame and this does not look as good as a link.
All you need do is create the blog and then create an external page link to your blog and that is it, no html snippets or fiddling around with any code. It is as simple as that.