You can download & install Picasa Web Album uploader for mac from
http://picasa.google.com/mac_tools.html. It works on iphoto 11. With it you should be able to upload photos into Picasa on the Web by going to File then Export. You can also subscribe to Picasa links on the web by clicking on the RSS link in Safari. Then copy the link. open iPhoto and then paste the link into "Subscribe to link" option under File. You should note that if the pics in the link change, your subscribed photos in iPhoto will change. So it's best to copy the pics into the photo library from the subscribed link to keep them permanently.