You should obviously increase the initial size of tempdb; one doesn't want autogrowth ocurring for any database, of course. You cannot truncate tempdb's log file because tempdb uses the simple recovery model.
From my experience, most 845 errors occur after someone monkeyed around with the server's configuration settings. If, however, your applications make heavy use of tempdb (e.g. Siebel), you may need to optimize the tempdb database: http://support.microsoft.com/?id=328551.