I use

  BACKUP LOG dbname WITH TRUNCATE_ONLY

  DBCC SHRINKFILE ('dbname_log', 1)

Good,

I have one table like this:

CREATE TABLE [CUSTOMER] (

 [COD] [bigint] NOT NULL,

 [NAME] [VARCHAR(50)] NOT NULL,

 CONSTRAINT [PK_COD] PRIMARY KEY  CLUSTERED  ([COD])

)

My table have 55.000 rows and my query is like this:

When i have to clear a log i use:

 BACKUP LOG DBNAME WITH TRUNCATE_ONLY

 DBCC SHRINKFILE ('LOGNAME', 1)

To do this you can use a 'Copy Databases Wizard' on Enterprise Manager!