So, I have iCal do the remembering for me:

Step 1  – Mute volume script in Leopard.

• Open Script Editor and type in this single line: set volume 0.
• Move it somewhere safe like your Documents folder (or ~/Library/Scripts/)

Step 2 — Classes in iCal.

• Make sure you’ve created events for your classes using iCal. (If you have, skip this step.)
• Double-click the event to see more options for that event, and have it repeat every week and end after 10 weeks.
• For MWF or TTh classes: if you have Leopard, you can set a Custom repeat and have it show up multiple days every week; otherwise, enter your classes multiple times and set each to repeat weekly.
  

Step 3 — Add script to event in iCal

In iCal, add an alarm for one of your classes. Set the type of alarm to Run Script, then select the script you saved in step 1. Set the alarm to run a short amount of time before the event. I set the alarm for 15 minutes before the event, so even if I’m late, the second I open my laptop, the volume is muted. Repeat for all your classes!

Note: if it prompts you to Change a recurring event, make sure you press All Future Events.

Mute system volume based on scheduled events in Mac OS X is a post from: My MacOS X