I finally took the time to rewrite this small script as a Movable Type plugin.
Here it is: download MT Comment Map
You can click on the map on right sidebar to see an example.
This plugin uses Geo::IP::PurePerl and HTML::GoogleMaps to display your comments on a google map. To use it, you need to install the two previous perl modules, and to copy paste your Google Map API key in the plugin settings. Then you can create a new index page with the following code:
<$MTCommentMapHead$> <$MTCommentMapDiv$> <$MTCommentMapScript$>
The <$MTCommentMapHead$> tag may take the following arguments: blog_id, height, width, zoom, type, lastn, max_comments_per_bubble.
Note that the free Geo::IP database is not very accurate, I’m not living in Lyon ;-)