Thanks to the sunbird/lightning developers you can download 
lightning-0.7-builds against libC05 or libC063 from
http://releases.mozilla.org/pub/mozilla.org/calendar/lightning/releases/0.7/contrib/os2/
Simply download and then install with the addons manager in Thunderbird

The LibC063 build works with every Thunderbird, Peter's enhanced or the 
official. The libC05 build works only with the official builds. However, I 
found that the libC05 build looks sluggish with the official 
Thunderbird-2.0.0.6 version, while it works well with the 2.0.0.4 version. 
So, if in doubt try  libC063.

"Lightning brings the Sunbird calendar to the popular email client, Mozilla 
Thunderbird. Since it's an extension, Lightning is tightly integrated with 
Thunderbird, allowing it to easily perform email-related calendaring tasks."

Have Fun
Walter Meinl