Hi,
I tried out the thunderbird_interface but getting a error in the OpenERP server log file.
The Thunderbird plugin is working I can find partners and so on, but when I press the archive button nothing happens.
The action so triggers an error in the log file as follows:

ERROR:web-services:[03]: System : Linux-2.6.24-24-server-i686-with-debian-lenny-sid
ERROR:web-services:[04]: OS Name : posix
ERROR:web-services:[05]: Distributor ID: Ubuntu
ERROR:web-services:[06]: Description: Ubuntu 8.04.3 LTS
ERROR:web-services:[07]: Release: 8.04
ERROR:web-services:[08]: Codename: hardy
ERROR:web-services:[09]: Operating System Release : 2.6.24-24-server
ERROR:web-services:[10]: Operating System Version : #1 SMP Tue Jul 7 20:21:17 UTC 2009
ERROR:web-services:[11]: Operating System Architecture : 32bit
ERROR:web-services:[12]: Operating System Locale : en_US.UTF8
ERROR:web-services:[13]: Python Version : 2.5.2
ERROR:web-services:[14]: OpenERP-Server Version : 5.0.7
ERROR:web-services:[15]: Last revision No. & ID :
ERROR:web-services:[16]: Traceback (most recent call last):
ERROR:web-services:[17]: File "/usr/lib/python2.5/site-packages/openerp-server/osv/osv.py", line 61, in wrapper
ERROR:web-services:[18]: return f(self, dbname, *args, **kwargs)
ERROR:web-services:[19]: File "/usr/lib/python2.5/site-packages/openerp-server/osv/osv.py", line 120, in execute
ERROR:web-services:[20]: res = pool.execute_cr(cr, uid, obj, method, *args, **kw)
ERROR:web-services:[21]: File "/usr/lib/python2.5/site-packages/openerp-server/osv/osv.py", line 112, in execute_cr
ERROR:web-services:[22]: return getattr(object, method)(cr, uid, *args, **kw)
ERROR:web-services:[23]: File "/usr/lib/python2.5/site-packages/openerp-server/addons/thunderbird_interface/partner/partner.py", line 48, in thunderbird_mailcreate
ERROR:web-services:[24]: case_pool._history(cr, user, cases, _('Archive'), history=True, email=False)
ERROR:web-services:[25]: NameError: global name '_' is not defined

Anyone knows a solution?

I have the same problem and error.
Outlook plugin works good

Problem solved!

Use the Thunderbird module from trunk addons!
I did use the old version from Extra-addons