The latest OS disk for the MkIV is V29.1 and you have two ways to get this loaded. You can either do it yourself or you can have you dealer do it for you. If you want to do it yourself, you can download it at
http://www.xoutpost.com/navigation-sy...available.html. If you are not comfortable doing it yourself, check with your dealer. Many (perhaps most) don't have a clue how to do this. Some will charge you an hour labor, others will do it free of charge. Your mileage may vary.
As for the lastest map disk, 2007.2 is the most recent version and you can buy it at
http://navteq.com for around $200.