Each night we will be doing a NET STOP, backing up our MDF, LDF, master and model databases, then doing a NET START. My ISP said that since we aren't using the SQL Server backup, that the LDF file will grow over time and affect preformance. He recommends reducing this file in size once per week. He used the word "truncate". A couple of questions.

1) Do I need to worry about the LDF's growing?
2) Is a truncate the same as the term "shrink" that I see in the Mgt Studio UI?
3) Is there a command that I can issue to accomplish this instead of going into the Mgt Studio UI once per week?