Picasa lacks of a serious multi file rename function. This project helps you with a Button for Picasa that will offer this missing function. Select the files you want to rename and simply click on the Rename Button. A Dialog let you choose all the details for renaming files.
Limitation: Picasa transfers each file with full pathname into the clipboard it depends on the directory structure how many files can be renamed at once.
Installation: Just unpack the zip to the Google\Picasa3\buttons...