Orkut has recently enhanced the find friends functionality on the profile page. Now you can add friends using email contacts in your external email accounts. Currently Hotmail and AOL email accounts can be used (Official Orkut blog mentions Yahoo as well, but I am unable to see Yahoo in the list). According to the official blog, more external email providers will be added to this list soon!
For adding contacts from external email accounts, you need to give your account id and password. If your contacts are using gmail and they are on orkut, you can directly add them after importing them. For contacts who are not on Orkut, you can send an invitation asking them to join Orkut.