JFBConnect on Joomla 1.7 uses the same database tables as Joomla 1.5. To migrate, we'd recommend you:
* Uninstall the Joomla 1.5 version (this just ensures all the files are properly removed and replaced with the 1.7 versions)
* Install the Joomla 1.7 version
* Check all your settings to make sure they're correct. For example, the content plugin no longer has 'Section' settings, so make sure the category settings are correct
Please note that Facebook's Like and Comment buttons work heavily off of the URL of the page they are on. Depending on where your Like/Comment widgets were, what extensions you're using, whether SEF is enabled (and whether it's Joomla's SEF or a 3rd party), the URL for a specific page may change. This can hurt your SEO rankings and can cause your Likes or Comments to not change over (since the URL is different).
Hope that helps, but generally, for JFBConnect, it's a simple reinstallation that's required.
Alex