here's what orkut blog posted, titled "Never miss a birthday again with orkut birthdays on Google Calendar"
Upcoming Birthdays is one of the most popular features we've added to orkut, but we recognize that it doesn't always give you all the information you need. It's great to know about birthdays coming up in the next couple weeks, but sometimes it's also important to see the birthdays that have already passed and the ones coming further down the line.
Now, in conjunction with Google Calendar, you can see all of your orkut friend's birthdays for the whole year.
If you've already used Google Calendar before, you will shortly see a link (right below the "upcoming birthdays" section) where you can add your orkut friends' birthdays to your Google calendar.
Once you've added your orkut birthday calendar to Google Calendar, you can navigate forward and backwards through time to see whose birthday is coming up and any birthdays you might have missed.
Although a very useful step but there's something missing that makes Google Calender so useful and its the SMS reminder feature it offers... you can get reminders for all the events in your main calender but not for the events in your orkut friends birthday calender, as a matter of fact there are no notification settings for this calender and also if you Google Calender gadget activated through Gmail Labs in your Gmail, this calender doesn't show up there too... so whats the use except that you can just see all the birthdays anytime you want..
As far as the title of the post on orkut blog is totally wrong, you can have all your orkut friends birthday in Google calender but yes you can still miss them because of no notifications...
There's one thing that you can do you can manually add every Orkut friends birthday to your main calender and to do that just click on and event in orkut calender and choose copy to your calendar option in the pop-up... So its something that will keep you busy if you have lots of friends...