[Orgmode] Date calculations

[Fredrik]

I'm using a normal org-file as my contact register so I easier can  
link tasks to a specific person. I have also added events as birthdays  
to each contact but is there some way I can make them show up in the  
agenda with some yearly calculations?

For example a simple birthday reminder can look like this:

* <2006-12-30 ++1y> Happy Birthday!

Is there some clever way I can add a date calculation to it when it  
shows up in the agenda?

* <2006-12-30 ++1y> Happy Birthday %d years!

Regards,

Fredrik