As far as I know, no one has gotten syncing working with box.net
If you want it working as soon as possible with the least headache, it may be worth paying for Mobile Me or BingoDisk. We've tested with iDisks, and several users report success with BingoDisk.
If you have a little more time, and a desktop or laptop mac, and want to save a little money, you might find this approach useful:
http://manas.tungare.name/blog/2008/...cus-to-iphone/