Here’s a quick and really neat trick for Mac users who would like to have birthdays listed in iCal. As default, your Mac will easily display birthdays in iCal, based on dates from your Addressbook, but it can’t give you an alarm and there’s no way to modify the events to do so.
So, somebody created an Automator workflow/application that will add your contact’s birthdays to iCal with an alarm you define, e.g. when to sound an alarm (2 days prior, etc.) or whatever you want it to do.
It’s freeware and you can download it here, from Apple Downloads, then just run it through Automator and it’s pretty self explanatory.