Quick help for those who want to manage their google calendars using Thunderbird: you can use the combination of Lightning addon (based on the Sunbird calendar one) and the Provider for Google Calendar addon.
I’m using here Ubuntu Jaunty (9.04) and Thunderbird 188.8.131.52, and I faced the following problem: after installing both addons, I wasn’t able to create a new calendar, it was showing greyed. So, after googling a little, I found out that one of the requirements for Lightning to work properly is the package libstdc++5, as you can see here. So, you need to install this package before installing Lightning.
sudo apt-get install libstdc++5
After that, just download the addons .xpi files and install them – In Thunderbird, Tools -> Addons -> Install… Restart Thunderbird as requested and when it opens again, you should see three buttons on the lower left, that are Mail, Calendar and Tasks.
Click on the Calendar one, and with right click you should have a Add Calendar… option. Note: you *must* be in the Calendar view to see it.
Click on it. You’ll need the Private XML address of your Google Calendar. To get it, go to your Calendar page on Google, and right click the arrow next to your calendar. Choose “Calendar settings”, and search for the Private address. Click on the XML orange button, and voila! There it is. Copy it and go back to Thunderbird.
After clicking in the “New Calendar..” option, choose “In the network” calendar, and then “Google”, and paste the address. It now should ask you your Google credentials, and if authenticated sucessfully, you should be asked to choose a name and a color for it to be displayed in Thunderbird. Lightning doesn’t import the name neither the color used in the web interface.
That’s it! Worked for me. Hope this helps!