I saw a posting recently of a DBA not being able to truncate a transaction log. I rememberred this script that I had, (downloaded from Microsoft Support many moons ago), which did the job for me. It basically filled the log with data, then truncated and shrank the log. All important points throughout the script are commented.
When doing bulk data changes it may be beneficial to disable indexes prior to starting the operation. Fortunately, SQL's rich metadata makes this very easy to automate in a robust fashion.