Use your Mac to upload photos!
Now there's two ways to upload your photos to Picasa Web Albums -- from directly within iPhoto or using drag-and-drop from a standalone application.
For iPhoto users
The Picasa Web Albums Exporter lives right inside iPhoto. Select photos, choose Export in the File or Share menu, and upload them directly to your web album.
For a standalone application
Use the Picasa Web Albums uploader -- just drag photos from the Finder and click the Upload button.