A practical workaround is to use Picasa’s built-in “Starred Photos” album rather than trying to write EXIF ratings directly from the .picasa.ini files.

In Picasa, open the “Starred Photos” album, select all starred images, and apply a tag/keyword to them. That tag can then be read by many other photo applications, including Lightroom and Bridge. Once imported there, you can filter by that tag and, if needed, batch-apply whatever star rating system the new software uses.

This preserves the important information—which images were starred—even if it doesn’t directly convert Picasa stars into EXIF ratings inside the files.