Everytime I do an update to OS X, I have to run these commands in Terminal, because the animated alarm clock in iCal is just obnoxious. (It also pulls precious CPU cycles.)
Taken from this hint at macosxhints.com
cd /Applications/iCal.app/Contents/Resources/iCal\ Helper.app/Contents/Resources/
sudo cp -p alarmclock.mov alarmclock-mov.BAC
sudo echo “” >alarmclock.mov
cd /Applications/iCal.app/Contents/Resources
sudo cp -p alarmclock.mov alarmclock-mov.BAC
sudo echo “” >alarmclock.mov