Currently Google Buzz only knows certain types of websites to connect to your Buzz feed. They need to be authenticated in both directions. So while Google has taken care of this in Blogger, you may have sites on Posterous and WordPress that you want connected.
These instructions are brief and straight to the point for people who are technically inclined to perform these kinds of configuration edits to their blogs. I take no responsibility for you screwing up your sites. But if you want to try this detailed process, here are the steps and reference sites.
1. You need to make your blog site, “Social Graph” aware by adding a specially formatted line of HTML to your website. See – http://code.google.com/apis/buzz/documentation/#connect
The best way to do this is by editing the site template for your blog. In WordPress that would be editing the theme’s index.php page. In Posterous you edit the Theme and click the Advanced TAB to create your own custom theme CSS/HTML template. Add the line near the top in the HEAD section.
2. As noted in the above link you also need to add your blog to your Google Profile. Be sure to click the “This page has a profle” when adding it.
3. Normally you need to wait for Google to crawl your site, to pick up on the above entered Social Graph HTML you just added to your blog site. However there is a way to convince Google to crawl your site right away. See – https://sgapi-recrawl.appspot.com/
If your site is not listed there, then you may want to use the Google Webmaster Tools to add your site to the Webmaster Tools system, which links up your blog to your Google account. This also requires an additional line of HTML to be added to your blog template code. See – https://www.google.com/webmasters/tools/home
Once you add your site to Google Webmaster Tools, you can go back to the Social Graph Crawler and you should see the site listed there and you can force Google to crawl your site.
4. Once this has all been completed, you should be able to “add connected sites” from within Buzz. All the blogs in your profile that are tagged with the “profile” checkbox AND have the above mentioned Social Graph API LINK tag in them will appear.
Like I said previously, this is a detailed process and all of it has to be set up perfectly in order for this to work. I’m unsure on how often Google polls your sites to import into Buzz, but so far my posts have made it in, but not immediately like with PubSubHubBub.
UPDATE: And then there is this: http://blog.posterous.com/integrating-posterous-and-google-buzz