Simply go to your Posterous dashboard, click "Settings" on the top right, then click the "Edit Theme" button and select the "Advanced tab". Now, all you have to do is paste one of the following snippets where you want the button to show up and click the "Save, I’m done!" button.
- Standard button:
- Tall button:
That’s all you have to do to integrate Google +1 to your Posterous.
If you want to host the script yourself, the source code is available on Github:
git clone https://firstname.lastname@example.org/olalonde/google-plusone-posterous.git